Sexually Transmitted Disease and Male Infertility: A Systematic Review

Review

–

Andrology

Sexually

Transmitted

Disease

and

Male

Infertility:

A

Systematic

Review

Mikkel

Fode

*

,

Ferdinando

Fusco

,

Larry

Lipshultz

,

Wolfgang

Weidner

a_{Department of Urology, Zealand University Hospital, Roskilde, Denmark;}b_{Department of Urology, Herlev and Gentofte Hospital, Herlev, Denmark;}

c_{DepartmentofNeurosciences, HumanReproductionand Odontostomatology,Universityof Naples‘‘Federico II,’’Naples, Italy;}d_{ScottDepartment of}

Urology,BaylorCollegeofMedicine,Houston,TX,USA;e_{DepartmentofUrology,PediatricUrologyandAndrology,JustusLiebigUniversityofGiessen,Giessen,}

Germany a v ai l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n al h o m e p a g e : w w w . e u r o p e an u r o l o g y . c o m / e u f o c u s Articleinfo Articlehistory: AcceptedAugust4,2016 AssociateEditor: JamesCatto Keywords: Infertility

Sexuallytransmittedinfections

Abstract

Context: Theoretically, sexually transmitted diseases (STDs) have the potential to disruptmalefertility;however,thetopicremainscontroversial.

Objective: TodescribethepossibleassociationbetweenSTDsandmaleinfertilityandto explorepossiblepathophysiologicmechanisms.

Evidenceacquisition: Weperformedasystematicliteraturereviewinaccordancewith thePRISMAguidelines.PubMed,Embase,andtheCochraneLibraryweresearchedfor articlespublishedbeforeJanuary1,2016,usingtheMeSHtermsforavarietyofSTDsand infertility.Thesearchwasrestrictedtohumanstudiesperformedinmenandpublished inEnglish.Studieswereincludediftheycontainedoriginaldataonapossibleassociation or a cause-and-effect relationship between STD and male infertility. Studies were consideredonlyiftheyincludedanappropriatecontrolgroupand/orcomprehensive laboratory data. Due to heterogeneity in the literature, a qualitative analysis was performed.

Evidencesynthesis: RelevantstudiesonChlamydiatrachomatis,genitalmycoplasmas, Neisseriagonorrhoeae,Trichomonasvaginalis,andviralinfectionswereidentified.Forall pathogens,thestudieswerecontradictoryandgenerallyoflimitedquality.Instudies confirming an association, there was a tendency for authors to perform multiple analyseswithoutappropriatecorrectionsandtosubsequentlyfocussolelyonoutcomes thatseemedtosuggestapositiveassociation;however,thebodyofliteraturethatdoes not confirman associationbetween STDs andmale infertility is alsoof inadequate quality.Thedataregardingpossiblepathophysiologicmechanismsareinconclusive.

Conclusions: There may be an association between STDs and male infertility of unknown genesis and possibly with different pathogenic mechanisms for different pathogens.Alternatively,someSTDsmaycausemaleinfertility,whereasothersmay not;however,thereishardlyastrongcorrelation.High-qualitystudiesofthesubjectare needed.

Patient summary: Sexuallytransmitted diseasesmaycause maleinfertility through unknownmechanisms;however,fromtheavailableresearch,wecannotbesurethat thereisanassociation,andmorestudiesareneeded.

#_{2016EuropeanAssociationofUrology.PublishedbyElsevierB.V.Allrightsreserved.}

* Corresponding author. Department of Urology, Zealand University Hospital, Roskilde, Sygehusvej

10,Dk-4000Roskilde,Denmark.Tel.+4526213800.

E-mail address:mikkelfode@gmail.com(M. Fode).

http://dx.doi.org/10.1016/j.euf.2016.08.002

1. Introduction

Infertilityisdefinedastheinabilityofacoupletoachieve pregnancydespiteunprotectedintercourseforaperiodof >12mo[1].Approximately15%ofallcouplesareinfertile, anditisestimatedthatamalefactorplaysaroleinabout halfofthecases[2].Thecomponentsofmalereproductive functionincludehormonalregulationofthehypothalamic– pituitary–gonadal axis, complete spermatogenesis, and unobstructed normalsperm transportandstorage. Theo-retically, sexually transmitted diseases (STDs) have the potentialtodisruptseveralofthesesteps.Nevertheless,the mainfocusinstudiedSTD-inducedinfertilitytendstobeon the female partner. This review aimed to describe the possible association between various STDs and male infertility.Inaddition,possiblemechanismsbywhichSTDs may influence male fertility have been explored and discussed.

2. Evidenceacquisition

Weperformedasystematicliteraturereviewinaccordance with the PRISMA guidelines. PubMed, Embase, and the CochraneLibraryweresearchedforarticlespublishedbefore January1,2016,usingtheMeSHtermsforavarietyofSTDs andinfertility(Fig.1).Thesearchwasrestrictedtohuman studiesperformedinmenandpublishedinEnglish.Studies wereincludediftheycontainedoriginaldataonapossible associationoracause-and-effectrelationshipbetweenSTD andmaleinfertility.Toreducebias,studieswereconsidered onlyiftheyincluded anappropriatecontrolgroup and/or comprehensive laboratory data. Titles and abstracts were screened, and the full text of relevant articles was subsequentlyreviewedbeforeinclusion.Theprimaryauthor (M.F.) performed the initial screening, and all authors approvedthefinalselection.Resultsoftheliteraturesearch areillustratedinFigure2.Weextracteddataregardingthe prevalenceofrelevantSTDs,fertilitystatus,andtraditional semenparametersaswellasanydataonseminalfunctional statusorpresenceofantispermantibodies.When nothing elsewasmentionedinthetext,infertilitywasdefinedasthe inability to conceive for a period of at least 12 mo, and fertility was defined as a history of parenthood and/or a currentlypregnantpartner.Instudiesinwhichparticipants werereportedtohavesymptomaticurinarytractinfections, thisdetailisspecificallymentioned.Duetoheterogeneityof

the study methods and data, no meta-analyses were performed.

3. Evidencesynthesis

StudiesinvestigatingSTDsandfertilitystatusand/orsemen quality are summarized in Tables 1–4 according to pathogenic agents. The studies are further described in the text. Studies investigating possible causative links betweenSTDsandinfertilityaredescribedinthetextonly. 3.1. Chlamydiatrachomatis

3.1.1. Chlamydiatrachomatis:studiesinvestigatingassociationwith infertility

Some studies have indicated that the incidence of chla-mydiamaybehigherininfertilemencomparedwiththose with normal fertility. In one such study, serum samples wereobtainedfrommenfrom52coupleswithunexplained infertilityandfrom72expectantfathers[3].Menfromthe infertile couples were significantly more likely to be seropositive for chlamydia antibodies at a high titer; however, there wasno differencebetween groupsinthe

(((((((((((((“Sexually transmitted diseases”[Mesh]) OR “Chlamydia trachomatis”[Mesh]) OR “Neisseria gonorrhoeae”[Mesh]) OR “herpes genitalis”[Mesh]) OR “Ureaplasma

urealyticum”[Mesh]) OR “Mycoplasma hominis”[Mesh]) OR “hepatitis B”[Mesh]) OR “hepatitis C”[Mesh]) OR “HIV”[Mesh]) OR “Treponema pallidum”[Mesh]) OR “herpes simplex”[Mesh]) OR “cytomegalovirus”[Mesh]) OR “Trichomonaas vaginalis”[Mesh]) AND “infertility”[Mesh]

Fig.1–ThefullsearchstrategyofMeSHtermsusedforsearchingPubMed.

517

•Records idenfied through database searching

503

•Records aer duplicates removed

94

•Full-text arcles assessed for eligibility aer screening of tles and abstracts

41

•Studies included in qualitave synthesis

43

•Studies included aer final screening of reference lists

Table 1 – Studies investigating Chlamydia trachomatis and fertility status and/or semen quality

Study(year) Studycharacteristics Mainfindings Majorlimitations

Greendaleetal (1993)[3]

Case–controlstudy

52menfrominfertilecouplesand 72fertilemen

Questionnairesandbloodsamples

Infertilemenweremorelikelytobe seropositiveforchlamydiaantibodies atatiter1:64(OR:3.4;95%CI,1.3– 9.1)

Thetiterof1:64wasnotpredefined Multipleanalysesperformed

withoutcorrections Joki-Korpelaetal

(2009)[4]

Case-controlstudy

90menfrominfertilecouplesand 190fertilemen

Bloodsamples

ChlamydialIgG(27.8%vs6.3%)andIgA (22.2%vs6.2%)wereelevatedinmen frominfertilecouples(p<0.001)

67/90coupleshadconfirmed femalefactorinfertility

Mazzolietal (2010)[5]

Cohortstudy

454menwithprostatitisresulting fromchlamydiaand707menwith prostatitisresultingfromother bacteria

Bloodsamplesandsemensamples

68.5%inthechlamydiagroupvs1.9% inthenonchlamydiagroupwere subfertileaccordingtoWHOcriteria (p<0.003)

–

Vezniketal (2004)[6]

Cross-sectionalstudy 627healthyspermdonors Semensamples

Chlamydiadetectedin21.7% Spermmorphologyandmotility

reducedinsampleswithchlamydia 37.0%vs43.2%normalforms(p=0.01)

and48.4%vs52.0%vs48.4%motility (p=0.05)

Multipleanalysesperformed withoutcorrections

Ouzounova-Raykova etal(2015)[7]

Case–controlstudy

281infertilemenand100fertile controls

Semensamples

PCRdetectedchlamydiain13.9%of infertilemenvs2%offertilemen(nop valuegiven)

Nodefinitionoffertilityor descriptionofhowparticipants wereincluded

Unclearifgroupswereotherwise comparable

Ouzounova-Raykova etal(2009)[9]

Case–controlstudy

60menfrominfertilecouplesand 40healthycontrols

Urethralswabsfrominfertilemen

Chlamydiawasfoundin5menfrom theinfertilecouplesandin1fertile man:RR3.3(95%CI,0.4–27;p=0.26)

Unclearhowchlamydiainfections wereassessedinhealthycontrols Authorsconcludethatchlamydia

infectionisassociatedwith infertility,althoughthisisnot supportedbyresults Al-Sweihetal

(2012)[10]

Case–controlstudy

127menfrominfertilecouplesand 188fertilemen

Semensamples

ChlamydialDNAdetectedinsemenof 3.9%ofmenfrominfertilecouplesvs 3.7%offertilecontrols(p>0.05)

–

Abusarahetal (2013)[11]

Case–controlstudy

93infertilemenand70fertilemen Urinesamples

PCRdetectedchlamydiain4.3%of infertilemenand1.4%offertilemen (p=0.284)

–

Treietal (2008)[12]

Retrospectivecohortstudy 17764menwhoreceivedchlamydia

testingbetweenin2001and2002 Reviewofmedicaldatabasesfrom

2001to2005

Infertilitywasdiagnosedin1.27%of chlamydia-positiveand1.00%of chlamydia-negativemen

AdjustedHR1.36(95%CI,0.93–2.00; p>0.05)

Individualmedicalrecordsnot assessed

Chlamydiastatusbefore 2001unknown

Likelypresenceofunrecognized chlamydia

Karinenetal (2004)[13]

Nestedcase–controlstudyanalysisof aprospectivelyfollowedbirthcohort (n=12231)

181menwithself-reportedtimeto pregnancyof12moand2controls withnormalfertilityforeachcase Questionnairesandbloodsamples

Nodifferencesingenitalinfections Nodifferencesinpresenceof

chlamydiaIgGantibodies Subanalysesshowingdifferencesin

specificantibodyserotypes

Multipleanalysesperformed withoutcorrections Fewparticipantswithspecific

serotypes

Conclusionnotinlinewithresults

Karinenetal (2004)[14]

Nestedcase–controlanalysisofa prospectivelyfollowedbirthcohort (n=12231)

52menwithself-reportedtimeto pregnancyof12moand2controls withnormalfertilityforeachcase Questionnairesandbloodsamples

HighertitersofIgAantibodiesto chlamydiaHsp10infertilemen (p=0.048)

Nodifferencesinothertiters

Multipleanalysesperformed withoutcorrections

Samraetal (1994)[15]

Case–controlstudy

135menrecruitedatmaleinfertility clinicsand88fertilemen

Bloodsamples,semensamples,and urethralsmears

Chlamydiawasfoundin9.6%of infertilemenand5.7%offertilemen (p=0.29)

Severalotherpotentialcausesof infertilitypresentinbothmenand women

Liuetal (2014)[16]

Case–controlstudy

621menfrominfertilecouplesand 615fertilemen

Semensamples

Chlamydiafoundin2.58%ofinfertile menand2.28%offertilemen (p=0.732)

Multipleanalysesperformed withoutcorrections

CI=confidenceinterval;HR=hazardratio;Hsp=heatshockprotein;Ig,immunoglobulin;OR=oddsratio;PCR=polymerasechainreaction;RR=relativerisk; WHO=WorldHealthOrganization.

proportions of patients whowere positive for chlamydia antibodies at any titer (54% vs 52%). Furthermore, there were no significant differences in semen characteristics betweenantibody-positiveand-negativeinfertilemen.The authorsspeculatedthathigh-leveltitersareamarkerofthe mostserious infectionswithpotentialtocauselong-term sequelae such as infertility. Nevertheless, there was no significantassociationbetweeneitherpreviousdiagnosisof genitourinarydiseaseorself-reportedgenitourinary symp-toms and infertility. Another study analyzed chlamydia immunoglobulin(Ig)GandIgAantibodiesintheplasmaof

90menfrominfertilecouplesandfrom190healthyblood donors[4].BothIgG(27.8%vs6.3%)andIgA(22.2%vs.6.2%) wereelevatedinmenfrominfertilecouples(p<0.001).In addition,semenmotilitywaslowerinmenfrom infertile coupleswithchlamydialantibodiesthanamongmenfrom infertilecoupleswithoutantibodies.Chlamydialantibodies werenotassociatedwithothersemenparametersanddid not affectresultsofinvitrofertilization.Interpretationof theresultsiscomplicatedbythereportthat23of90couples hadmalefactorinfertility,whereas67of90hadconfirmed femalefactorinfertility,withnosignificantdifferenceinthe

Table 2 – Studies investigating genital mycoplasma species and fertility status and/or semen quality

Study(year) Studycharacteristics Mainfindings Limitations

Samraetal (1994)[15]

Case–controlstudy

135menrecruitedatmaleinfertility clinicsand88fertilemen

Bloodsamples,semensamples,and urethralsmears

Mycoplasmaspecieswerefoundin31.8%of infertilemenand28.4%offertilemen(not significant)

Consideredalone,MHwasfoundin13.3%of infertilemenand1.1%offertilemen (p<0.0015)

Nodifferenceinprevalencewhenconsidering UUalone

Multipleanalysesperformed withoutcorrections

Liuetal (2014)[16]

Case–controlstudy

621menfrominfertilecouplesand 615fertilemen

Semensamples

MHfoundin5.98%ofinfertilemenand4.88% offertilemen(p=0.472)

UUfoundin26.57%ofinfertilemenandin 24.88%offertilemen(p=0.496)

Multipleanalysesperformed withoutcorrections

Leeetal (2013)[26]

Case–controlstudy

50menfrominfertilecouplesand 48fertilemen

Semensamples

MHfoundin48%ofinfertilemenand25%of fertilemen(p=0.022)

UUfoundin14%ofinfertilemenand6.3%of fertilemen(p=0.318)

Multipleanalysesperformed withoutcorrections

Xuetal (1997)[27]

Case–controlstudy

1461menwithidiopathicinfertility and375fertilecontrols

Semensamples

UUfoundin38.77%ofinfertilemenand9.06% offertilemen(p<0.001)

–

Zeighamietal (2007)[28]

Case–controlstudy

100infertilemenand100healthy controls

Semensamples

UUfoundin12%ofinfertilemenand3%of fertilemen(p<0.05)

AnincreasedincidenceofUUininfertilemen (12%vs3%,p<0.05)

Nodefinitionoffertilityor descriptionofhowparticipants wereincluded Nodemographicinformationon participants Wangetal (2006)[29] Cross-sectionalstudy

346menattendingandrologyclinics Questionnairesandsemensamples

UUfoundin12%

UUinfectionassociatedwithhighersemen viscosity,lowersemenpH,andreducedsperm concentration(allpvalues<0.05)

UUinfectionwasnotsignificantlyrelatedto othersemenparameters

Multipleanalysesperformed withoutcorrections

Pleckoetal (2014)[30]

Case–controlstudy

145infertilemenand49fertile controls

Questionnairesandurinesamples

HistoryofSTDreportedby55.8%ofinfertile menand24.4%offertilemen(p=0.0001) Infertilemenhadahighernumberoflifetime

sexualpartners(p<0.0001).

Ureaplasmaspeciesfoundin30%ofthe infertilemenand35%ofthefertilemen(not significant)

MHfoundin21%ofthe

infertilemenand20%ofthefertilemen(not significant)

Riskofrecallbias

MH=Mycoplasmahominis;STD=sexuallytransmitteddisease;UU=Ureaplasmaurealyticum.

Table3–StudiesinvestigatingNeisseriagonorrhoeaeandfertilitystatusand/orsemenquality

Study (year) Study characteristics Main findings Limitations

Abusarah etal(2013)[11]

Case–controlstudy

93infertilemenand70fertilemen Urinesamples

Neisseriagonorrhoeaefoundin6.5%ofthe infertilemenandinnoneofthefertilemen (p<0.05)

–

Osegbe(1991)[35] Prospectivecohortstudy

45menwithgonococcalepididymo-orchitis Questionnaires,semensamples,bloodsamples

14/45menhadpreviouslyfatheredchildren 2yrafterthegonococcalinfection,21%ofthe

fathersand40%ofthewholegroupshowed normalsemenparameters

Semenparametersbefore infectionunknown

prevalence of antibodies betweenthese groups. A larger studyinvestigatedsemen qualityinmen withprostatitis resultingfromchlamydia(n=454)andfromotherbacteria (n=707) [5]. Sperm concentration, sperm motility, and normalmorphology were all significantlyreduced in the chlamydia-infected group (all p values <0.001). Overall, 68.5%inthechlamydiagroupand1.9%inthenonchlamydia groupwereconsideredsubfertileaccordingtoWorldHealth Organization(WHO)criteria(p<0.003). Similarly,Veznik

etalfoundthatspermmorphologyandmotilitywerehigher insampleswithoutchlamydiacomparedwith chlamydia-positivesamplesin627healthyspermdonors,with43.2% versus 37.0% normal forms (p=0.01) and 52.0% versus 48.4% motility (p=0.05), respectively [6]. Therewere no statistically significant differences in volume of semen, densityofthespermatozoa,ormeasuredspermmotility.

Consideringmixedinfections,Ouzounova-Raykovaetal investigatedthe prevalenceof polymerasechainreaction

Table 4 – Studies investigating sexually transmitted viral infections and fertility status and/or semen quality

Study(year) Studycharacteristics Mainfindings Limitations

Naumenkoetal (2014)[39]

Cross-sectionalstudy

232menattendinginfertilityclinics Semensamplesincludingtestsfor

EBV,CMV,andHHV-6

CMVwasmoreprevalentinthegroupof infertilemenwithchronicinflammatory urogenitaltractdiseasescomparedwiththe othergroupscombined(18.5%vs5.4%, p=0.03)

CMVwasassociatedwithreducedsperm count(39.5vs72.5106_/ml,p=0.036)

HHV-6wasmoreprevalentinfertilemen withchronicurogenitaltractinflammation thanintheothergroupscombined(19%vs 6.3%,p=0.018)

Noothersignificantrelationships

Nodefinitionoffertility Multipleanalysesperformed

withoutcorrections Forestaetal (2010)[40] Cross-sectionalstudy 200menaged18yr Semensamples

HPVwasassociatedwithreducedsperm motility(53.7%inHPV-negativevs37.7%in HPV-positive;p<0.05)

Othersemenparametersdidnotdifferwith orwithoutHPV

Multipleanalysesperformed withoutcorrections

Authorsdidnotinvestigatethe presenceofotherviruses Suetal(2014)

[41]

Retrospectivecase–controlstudy 5138menwithHBVand25

690noninfectedcontrols DatafromtheTaiwanNational

HealthInsuranceResearchDatabase

HBVinfectionassociatedwithanincreased 10-yrincidenceofinfertilitydiagnosis(HR: 1.52;95%CI,1.20–1.92;p<0.05)

Individualmedicalrecordsnot assessed

Likelypresenceofunrecognized HBV

Limitedcorrectionforconfounders Morettietal

(2008)[42]

Case–controlstudy

15menwithchronicHBV,13men withchronicHCV,and20fertile controls

Semensamples

Nodifferencesinspermconcentration, motility,ormorphologybetweenpatients andcontrols

Increasedincidencesofspermnecrosisin infectedmen(43.2%forHVC,35.86%for HBV,and15.57%fornoninfectedmen; p<0.01)

Increasedincidencesofspermapoptosisin infectedmen(6.76%forHVC,7.5%forHBV, and2.9%fornoninfectedmen;p<0.05)

Multipleanalysesperformed withoutcorrections

Hofnyetal (2011)[43]

Case–controlstudy

57HCVinfectedmenand40fertile controls

Semensamples

MeansemenvolumeincreasedwithHCV: 2.33vs2.15ml(p<0.05)

MeanspermcountreducedwithHCV: 40.1vs75.4106

/ml(p<0.01)

Meanspermabnormalformsincreasedwith HCV:40.35%vs12.6%(p<0.01)

MeanspermmotilityreducedwithHCV: 39.6%vs58.1%(p<0.01)

Controlparticipantshadconfirmed fertilitybeforeenrollment,whereas thefertilitystatusofparticipants withHCVwasunknown

Mulleretal (1998)[44]

Case–controlstudy

250HIV-seropositivemenand 38fertilecontrols

Semensamples

MediansemenvolumereducedwithHIV: 1.8vs2.9ml(p<0.0001)

Medianspermconcentrationreducedwith HIV(62vs100106

/ml,p<0.001) MedianspermmotilityreducedwithHIV:

52%vs64%(p<0.0001)

Medianrapidandlinearmotilityreduced withHIV:14%vs21%(p<0.05)

Controlparticipantshadconfirmed fertilitybeforeenrollment,whereas thefertilitystatusofparticipants withHIVwasunknown

Umapathy (2005)[46]

Cross-sectionalstudy

83apparentlyhealthymenattending ahospitalforundisclosedreasons Semensamplesandbloodsamples

36/83testedHIVpositive

MeanspermmotilityreducedwithHIV:34% vs53%(p<0.02)

Nodifferenceinspermcountandsperm morphologybetweeninfectedand noninfectedmen

Nodemographicknowledge provided

Unclearwhyhealthymenwould visitahospital

CI=confidenceinterval;CMV=cytomegalovirus;EBV=Epstein–Barrvirus;HBV=HepatitisBvirus;HCV=HepatitisCvirus;HHV-6=Humanherpesvirus6; HIV=humanimmunodeficiencyvirus;HPV=humanpapillomavirus;HR=hazardratio.

(PCR)–detectedchlamydia,Mycoplasmahominis(MH),and Ureaplasmaurealyticum(UU)insemenof281infertilemen and100fertilecontrols[7].Prevalenceofallpathogenswas increased in infertile men, with chlamydia, UU, andMH foundin13.9%,19.2%,and9.9%,respectively,versus2%,11%, and 3%, respectively, in fertile men (no p values given); however, the authors did not include their definition of fertilityorhowparticipantswereincluded.Inaddition,no descriptionofotherpossiblediscrepanciesbetween infer-tileandfertilemenwasgiven.Anotherstudyinvestigated whether coinfection with chlamydia andhuman papillo-mavirus(HPV)affectedspermparametersin1003menwith chronicprostatitis[8].Atotalof71.3%ofthepatientswere infectedwithchlamydiaonly,and28.7%wereinfectedwith bothchlamydiaandHPV.Onsemenanalysis,50.8%inthe chlamydia-onlygroupversus66.8%inthecoinfectedgroup weresubfertileaccordingtotheWHOcriteria(p<0.001). Thefindingthatalmostone-thirdofthechlamydia-infected menwerecoinfectedwithHPVunderscoresthatSTDsoften coexistandmaypotentiateeachother’sdetrimentaleffects. Thestudyislimitedbyalackofacontrol groupinfected with onlyHPV, whichmeansthat itis difficultto assess whether the reduced semen quality was caused by the coinfectionorbyHPValone.

Otherstudieshavebeenunabletoidentifyanassociation between chlamydia and male infertility. A study by Ouzounova-Raykovaandcoworkersinvestigatedthe preva-lenceofchlamydiain60malepartnersofinfertilecouples comparedwiththeprevalencein40healthycontrols[9].The authorstookurethralswabsfromallmaleparticipantsand cervicalswabsfromthefemalepartnersofinfertilecouples and used cultures and PCR for chlamydia detection. Chlamydiawasfoundinfivemenfromtheinfertilecouples andinonecontrolparticipant(p=0.26).Threeofthefemale partnersof chlamydia-positive men harboredsigns of an infection. For a similar study of 315 participants, the investigators detected chlamydial DNA in the semen of 3.9% of men from infertile couples versus 3.7%of fertile controls(p > 0.05)[10]. Thestudy showedbetter semen parametersinuninfectedmencomparedwithinfectedmen in the fertile subgroupbut not in the infertile subgroup. AbusarahetalalsousedurinePCRfordetectionofchlamydia in93infertilemenwithabnormalsemenparametersand 70menwhohadpreviouslyfatheredchildrenand/orhada normalspermevaluation[11].Theyfoundchlamydiain4.3% of infertile men and 1.4% of fertile men (p=0.284). It is unclear whether the groups were comparable because controlswererecruitedamong menpresentingaturology clinicsforundisclosedreasons.

Althoughmoststudiesarecomposedmainlyofclientsof infertility clinics who likely suffer competing causes of infertility, two database studies have looked at the association between chlamydia and the development of infertility.Treietalusedlaboratoryrecordstoidentifyall active-dutyAirForcemenwhoreceivedchlamydiatesting betweenin 2001and2002(n=17 764)[12].Participants weretrackedthrough2005,andinfertilitywasdiagnosedin 1.27% of chlamydia-positive and 1.00% of chlamydia-negative men. The difference did not reach statistical

significance.Karinenetalconductedasimilarstudywith data from a prospectively followed Finnish cohort of 12 231 men and women [13]. Participants consisted of thosewhobothdeliveredbloodsamplesandrespondedto questionsabouttheirtimetopregnancyattheageof31yr. Overall,181menand298womenhadself-reportedtimeto pregnancyof12mo.Tworandomcontrolswithnormal fertility werepicked for eachcase. The studyshowed no statistically significant differences in either self-reported genital infections or the presence of chlamydia IgG antibodies between the cases and controls. Only after various subanalyses of 10 different serotypes were the authors able to demonstrate an increased occurrence of antibodies in male cases demonstrating a C complex containingimmunotypesC,J,H,andI(7.7%inmalecases and3.0%incontrols;p=0.012)andinindividualserotypeH among men (p=0.036) and serotypes C (p=0.036), J(p=0.022),H(p=0.021),andI(p=0.025)amongwomen. Theremainingassociationswereinsignificant.Despitethe multipleanalysesperformedandthelowabsolutenumbers of participants with specific serotypes, the authors still hypothesizedthat‘‘chlamydiainfectionplaysanimportant roleinmaleinfertility.’’

In asubsequentstudyofthesamecohort, theauthors looked at a possible association between infertility and antibodiesto chlamydia heatshock protein(Hsp) 60and Hsp10 [14]. Using 146 cases (94 women and 52 men) and 278controls (188 women and90 men),the authors foundthatIgAantibodiestochlamydiaHsp60andHsp10 were significantly higher in female partners of infertile couples comparedwith controls (p=0.002and p=0.007, respectively),whereastherewasnostatisticallysignificant difference in IgGantibodies to the two proteins. Among men, thecontrolparticipantsshowed significantlyhigher titersofIgAantibodiestoHsp10(p=0.048),whereasthere werenodifferencesintheremainingtiters.Takentogether, thetwostudiesintheFinnishcohortdonotshowaclear linkbetweenchlamydiainfectionandmaleinfertility.

Regarding mixed infections, Samraet allooked atthe prevalence ofchlamydia,UU,andMHininfertile couples (n=135)andfertilecouples(n=88)[15].Amongthemenin infertile couples, oligoteratoasthenozoospermiawas diag-nosedin62.9%,with28.9%havingavaricocele.Inaddition 21.5%ofthemenwerediagnosedwithprostatovesiculitis, antispermantibodies,orboth.Amongwomenfrominfertile couples, ovulatory dysfunction was diagnosed in 31.8%, tuboperitoneal adhesionsand/orendometriosiswas diag-nosed in 6.7%, and uterine adhesions or myomata were diagnosedin5.2%.Thedegreeofoverlappingpathologyin couples is unclear. Antichlamydia IgA, IgG, and IgM antibodiesweretestedinbloodandsemen,whereassemen, urethral, and cervical smears were cultured for bacteria. Chlamydiawasfoundin9.6%ofmenand10.4%ofwomenin theinfertilegroupandin5.7%ofmenand4.5%ofwomenin thefertilegroup(p=0.29andp=0.12,respectively).More infertile women were positive for serum chlamydia IgG compared with fertile women(11.9% vs 3.4%, p<0.015). Likewise,specificsemenIgAwashigherininfertilethanin fertilemen(8.9%vs1.1%,p<0.015).However,therewere

nodifferencesintheprevalenceofremaining immunoglo-bulins, and no corrections were made for multiple comparisons.AsimilarstudyusingPCRfoundnosignificant differences in the prevalence of the three pathogens in semenbetween 621men from infertile couples (34.93%) and615fertilecontrols(32.03%)[16].

3.1.2. Chlamydiatrachomatis:studiesinvestigatingpossible causativelinkstoinfertility

Despite the questionable link between infertility and chlamydia, several studies have attempted to identify causative mechanisms. A direct toxic effect has been suggested by in vitro experiments. In one such study, Galdiero and coworkers showed that lipopolysaccharide extractedfromchlamydiacausedspermatozoamortalityof 100%within 60min ofincubation [17]. Likewise, another studyfoundthatincubatingspermatozoafrom normosper-matic men with chlamydia elementary bodies caused a declineinmotilespermcellsandanincreaseindeadcells

[18].Whenincubatingspermwithdeadelementarybodies, thedetrimentaleffectswereabolished,indicatingthatthese detrimental events were caused by live bacteria only. Regarding advanced sperm function, limited data from a study of 293 infertile men of whom 13% had signs of previouschlamydiainfectiondidnotpointtoanassociation between chlamydia and reduced sperm DNA integrity

[19]. Meanwhile, astudyassessingtheacrosomereaction insemenfromchlamydia-negative(n=46)and chlamydia-positive (n=30) male partners of infertile couples and healthy men (n=53) suggested that sperm functional capacity may be reduced with infection [20]. Other researchers have investigated a possible autoimmune responseagainstspermcells,withunconvincingresults[21]. An alternative theory of cause and effect is that chlamydial infections may cause damage to the ductal system.Totestthistheory,SripadaetalusedPCRtodetect chlamydia DNA in testicular/epididymal biopsies and aspirateof14menwithidiopathicobstructiveazoospermia and22menseekingvasectomyreversal[22].No chlamydia-specific DNA was detected in any of these participants, making the hypothesis that asymptomatic chlamydial infectioncanleadtoobstructionofthemalegenitaltract unlikely.However,thislackofcausationmaynotapplyto menwithsymptomatic chlamydiainfections.In addition, theprevalenceofchlamydiainthebackgroundpopulation wasuncertain, andthe authorsdid notperform a power analysis,meaningthatthestudy couldhavebeen under-powered. Looking for more subtle signs of damage, Gonzalez-Jimenezetalfoundthatinfertilemenwithfree stereociliainsemenhadincreasedprevalenceofchlamydia, MH,andUUonsemenculture[23].Thisresultwastakenas indirectevidencethatinfectionsmaycausedamagetothe ductal system. However, the small number of highly selectedparticipants makesthe study prone to bias, and theauthorsconcludedthatprospectivetrialsareneededto confirmthehypothesis.

Yetanothertheoryrevolvesaroundthefemalepartner. Eggert-Kruseetalfoundasignificantrelationshipbetween thepresenceofchlamydiaantibodiesinmen’ssemenand

tubalinfertilityintheirfemalepartners(n=197)[24].The finding was confirmed in a subsequent study with 1303couplesconsultingforinfertilitytreatment[25].There wasnorelationbetweenchlamydiaantibodiesandgeneral semenquality,spermfunctionalcapacity,orthepresenceof antispermantibodiesineitherofthestudies.Thefindings suggestthatchlamydiadoesnothaveadirecteffectonmale fertilitybutratherhasanindirecteffectthroughinfectionof thefemalepartner.

3.2. Genitalmycoplasmaandureaplasmaspecies 3.2.1. Genitalmycoplasmaandureaplasmaspecies:studies investigatingassociationwithinfertility

InthestudybySamraetal,describedabove,mycoplasma specieswerefoundin31.8%ofmenand25.9%ofwomenin infertilecouplesandin28.4%ofmenand26.2%ofwomenin fertile couples [15]. Neither difference was statistically significant. However, when considered alone, MH was foundin13.3%ofinfertilemenand10.4%ofinfertilewomen and in only 1.1% each of fertile men and women (p<0.0015 and p<0.01, respectively). In contrast, Lee etalfoundthatUUwasmorefrequentinsemenfromthe men from 50 couples with idiopathic infertility (48%) compared with 48 fertile men (25%; p=0.022), whereas there were no significantdifferences betweenthe occur-renceofMH[26].

AlargerstudylookedatUUin1461menwithidiopathic infertilityand375fertilecontrols,allwithnormalsemen parametersaccordingtoWHO1987criteria[27].Therewas a significantly higher frequency of UU infection among infertile men compared with fertile controls (38.77% vs 9.06%, P<0.001). Examination of eight specimens from infertilemenandeightspecimensfromfertileparticipants byelectronmicroscopy,immunogold,and immunofluores-cence techniques demonstrated adhesion of UU to the membranes of spermatozoa and exfoliated germ cells, which the authors proposed as a possible cause of the infertility. An increased incidence of UU in semen from 100infertilemencomparedwith100healthycontrols(12% vs 3%, p<0.05) analyzed using PCR was also found by Zeighami etal [28]. In theUU-positive infertile patients, semen volume, count, and normal morphology were reducedcomparedwithUU-negativeinfertilemen. Unfor-tunately,thestudydidnotprovidedemographic informa-tionontheparticipants,andthestudydefinitionsofinfertile and fertile men were not provided. These findings are somewhat contradictedby anearlier study in whichthe relationshipbetweenUUandsemenqualitywasassessedin 346menattendingChineseandrology clinics[29].Inthis study, 39.3% had positive semen UU cultures, and on multivariate analysis, this was associated with higher semen viscosity, lower semen pH, and reduced sperm concentration (allpvalues<0.05).However,UUinfection was not significantly relatedto othersemen parameters. Another studycomparedtheoccurrenceofgenital myco-plasmasinfirst-voidurinesamplesfrom145infertilemen withreducedsemenqualityand49fertilecontrols[30].The infertile men were significantly more likely to report a

history of STD (p=0.0001) and had a higher number of lifetime sexual partners (p<0.0001). Nevertheless, the studyrevealednostatisticallysignificantdifferencesinthe occurrenceofMHandUUbetweenthegroups.

3.2.2. Genitalmycoplasmaandureaplasmaspecies:studies investigatingpossiblecausativelinkstoinfertility

As with chlamydia, the possible pathophysiology behind MH-or UU-relatedinfertility hasbeen investigatedin in vitro studies. Dı´az-Garcı´a and coworkers showed that clustersofMHattachtospermatozoaandlocate intracellu-larly[31]. Interestingly, theMH–spermatozoa interaction reachedamaximumwithinthefirsthourandthenstarted to decline. Sperm viability did not decline significantly comparedwithuninfectedspermatozoa.Likewise, Nunez-Calongeetalfoundasignificantreductioninspermmotility aswellassignsofmembranealterationswhenincubating spermatozoawithUU[32]. Scanningelectronmicroscopy showed that clusters of UU attached to the deformed spermatozoa. In a more complex study, Reichart et al furtherconfirmedthatUUadheretospermcellsinvitroand thatinfectioncauseddose-andtime-dependentchromatin decondensation and DNA damage [33]. Surprisingly, infectedcellsexhibitedhigherratesofviabilityandmotility than uninfected cells. The study also investigatedsperm chromatinstabilityandDNAintegrityinsemenfromeight men with UU-positive cultures. Initially, the sperm cells exhibited a low percentage of stable chromatin, as determined by nuclear chromatin decondensation assay (42%,n=8),andahigh percentageof denaturedDNA, as determined by sperm chromatin structure assay (60.9%, n=7).Asignificantimprovementinbothparameterswas observedfollowing10dofdoxycyclinetreatment.Contrary to this finding, another study measured susceptibility of DNAstrandbreaksinsperm nuclearchromatinto insitu denaturationin293menandfoundnooverallassociation with chlamydia, UU, and MH infection [19]. Antibiotic therapywasinitiatedandfollowedupin47oftheinfected menwithnoapparenteffectonsemenparameters.

Adifferentapproach wastaken by Shiandcoworkers whorecruitedhealthydonorsandinfertilepatientsinfected with UU [34]. Using western blot analyses, the authors confirmedtheexistenceofpossiblecross-reactiveantigens betweenUU and human sperm membrane proteins. The authors were able to purify one of the cross-reactive antigens and identify a common pentapeptide between urease complex component UreG and human nuclear autoantigenic sperm protein. The clinical significance of thisfindingisunclear.

3.3. NeisseriagonorrhoeaeandTreponemapallidum

Our search yielded only two studies demonstrating a possible association between Neisseria gonorrhoeae and male infertility. In the Jordanian study, previously de-scribed,involving93infertilemenand70fertilecontrols, NeisseriagonorrhoeaeDNAwasdetectedinsemenfrom6.5% ofinfertile menandinnoneofthefertile men(p<0.05)

[11].Inanother study,thefertilitystatusof45 menwho

developed gonococcal urethritis and subsequent epidi-dymo-orchitiswere followedprospectively[35].Fourteen ofthemenhadpreviouslyfatheredchildren;however,2yr afterthegonococcalinfection,only21%ofthesefathersand 40%ofthewholegroupshowednormalsemenparameters. Althoughseveresyphilisinfectionscanlikelycauseductal obstruction and/or testicular damage, no studies on Treponema pallidum were deemed appropriate for this review.Thelackofstudies onthetwopathogensislikely duetotherarityofinfectionsindevelopedcountries. 3.4. Trichomonasvaginalis

Limited evidence from in vitro studies suggests that Trichomonas vaginalis may have detrimental effects on sperm motility [36,37]. Onlya singlestudy investigating possible in vivo effects was identified, but the authors selected an inappropriate control group with confirmed normalsemenparameters[38].

3.5. Sexuallytransmittedviralinfections

3.5.1. Epstein–Barrvirus,cytomegalovirus,humanherpesvirus,and humanpapillomavirus

Naumenko et al looked at Epstein–Barr virus (EBV), cytomegalovirus (CMV), and Human herpesvirus 6 (HHV-6)DNAinsemensamplesof232menattendinginfertility clinics [39]. This cohort consisted of infertile men with varicocele, men with idiopathic infertility, infertile men with chronic urogenital tract inflammation, fertile men withchronicurogenitaltractinflammation,andmenwhose partners had a history of pregnancy loss. The total prevalence of PCR-detected viral DNA was 17.7%. CMV was more prevalent in the group of infertile men with chronic inflammatoryurogenital tract diseasescompared withtheothergroupscombined(18.5% vs5.4%,p=0.03). Furthermore, CMVinfectionwasassociated withreduced spermcount(39.5vs72.5106_{/ml,p=0.036).Incontrast,}

HHV-6 was more prevalent in fertile men with chronic urogenital tract inflammation than in the other groups combined(19%vs6.3%,p=0.018),buttheinfectionwasnot associated with any differences in semen parameters compared with the remaining groups. No associations betweenEBVandinfertilityorurogenitaltract inflamma-tion werefound.The studyislimitedbythefactthatthe authorsfailedtodescribehowfertilemenweredefinedand why fertile men would visit an infertility clinic. No corrections for multiple comparisons were performed. In abetterdesignedstudy,Forestaandcoworkersinvestigated theprevalenceofHPVin200volunteersaged18yr,100of whom had previously had sexual intercourse [40]. Not surprisingly, none of those without intercoursehad HPV DNAintheirsemen.Theprevalencewas10%inthesexually activeparticipants.Seminalvolume,pH,sperm concentra-tion, viability, and normal morphology did not differ betweenHPV-infectedandnoninfectedparticipants; how-ever,HPVwasassociatedwithsignificantlyreducedsperm motility(53.7% inHPV-negative vs37.7%in HPV-positive participants; p<0.05). Although the authors excluded

bacterialinfectionsbymicrobiologicalspermculture,itis importanttonotethattheydidnotinvestigatethepresence ofotherviruses,meaningthatcoinfectioncouldbepresent insomeoftheparticipants.

3.5.2. Hepatitis

SuetaluseddatafromtheTaiwanNationalHealthInsurance ResearchDatabasetocomparetheincidenceratesofmale infertility in5138 men withnewly diagnosed Hepatitis B virus(HBV)and 25690 noninfectedcontrols[41]. With a follow-up period of 10 yr, the study found a 1.59-times increased crude incidence rate of infertility in the HBV patients, corresponding to an overall risk in the infected group of 1.83% versus 1.15% in the noninfected group (p<0.05). Theassociation remained significanton multi-variateanalysis(hazardratio:1.52;95%confidenceinterval, 1.20–1.92).Inamuchsmallerstudy,thespermqualityfrom patientswithchronicHBV(n=15)orHepatitisCvirus(HCV; n=13)andunknownfertilitystatuswascomparedwiththat of 20 fertile controls [42]. There were no statistically significant differences in traditional semen parameters, but increased incidences of apoptosis and necrosis were observedininfectedmenbyelectronmicroscopy.Another study looked at the possible effect of HCV on semen parametersin57infectedmenand40fertilecontrols[43].In thatstudy, the duration ofHCV infection was negatively correlatedwithsemenvolumeandspermmotility,andthe viralloadwasnegativelycorrelatedwithspermcountand spermmotility.HCV-infectedpatientsalsohadsignificantly lowertotal serum testosterone and higherserum E2 and prolactinlevelscomparedwithhealthycontrols.

3.5.3. Humanimmunodeficiencyvirus

Apossibleeffectofhumanimmunodeficiencyvirus (HIV) was assessed by Muller and coworkers through semen analyses in 250 HIV-seropositive men and 38 fertile controls[44].Thefertilecontrolshadsignificantlygreater semenvolume(2.9vs 1.8ml, p<0.0001),sperm concen-tration(median100vs62106_{/ml,p<0.001),percentage}

ofmotility(median64%vs52%,p<0.0001),andpercentage ofrapidandlinearmotility(median21%vs14%,p<0.05) than HIV-seropositive men. Nevertheless, there was no differencebetweenthegroupsintheproportionofsperm with normal morphology and the number of leukocytes insemen. InthegroupofHIV-positive men, CD4+ _values

<200/mm3 _{were associated with significantly lower}

proportions of motile spermatozoa, strictly normal mor-phology, and total morphologically normal spermatozoa. Likewise,based on clinical categories, healthiermen had significantlyhigherproportionsofstrictlynormal morphol-ogy, andfewer had azoospermia.The authors concluded that HIV-seropositive men with low CD4+ _{cell counts or}

severe symptoms had reductions in semen quality that weresimilartothoseofothermenwithchronicdiseases. Similar findings were made in a subsequent study that investigatedtheeffectsofdifferentpatientcharacteristics on fertilizing capacity in 33 HIV-seropositive men

[45].Spermvitality,motility,andpenetrationratesassessed bythezona-freehamsteroocytepenetrationtestwereall

correlatedwithCD4+cellnumber,andtheparameterswere significantlyhigherinpatientswhoseCD4+_countswereat

least 350/mm3_{compared withthose whose CD4}+ _counts

were<350/mm3(allpvalues<0.05).Interestingly,sperm penetrationrateinpatientsreceivingantiretroviraltherapy wassignificantlyhigherthaninthosenotreceivingantiviral therapy,implyingthatthetreatmentcouldbebeneficialfor fertility (p < 0.05). A simpler study was performed in Zimbabwe bycollectingspermandbloodfrom83 appar-ently healthy men attending a hospital for undisclosed reasons [46]. Sperm motility was impaired (34% vs 53%, p<0.02)inHIV-positivemen,whereasneitherspermcount norsperm morphologydifferedsignificantlybetweenthe groups.Thepaperdidnot provideinformationon clinical fertilitystatus.

4. Conclusions

The available literatureexploring a possible association betweenSTDsandmaleinfertilityisoflimitedquality,and the results are contradictory. Studies confirming an association more frequently tended to have significant drawbacks.Therewasatendencyforauthorstoperform multipleanalyseswithoutappropriatecorrectionsandto subsequently focus solely on outcomes that seemed to suggest a positive association; however, the body of literature thatdoes notconfirman association between STDsandmale infertilityisalsoofinadequatequalityto drawanyfinalconclusions.Asignificantlimitationinthe literature is that only a few studies have investigated symptomaticSTDs. Serum analysisforIgG, for example, may reflect an interaction with a pathogen but not necessarily a relevant inflammatory response that can altertheanatomy orphysiologyofthegenitaltract.This might contribute to the wide differences found in the literature.Forthesereasons,wecannotexpecttheexisting literature to unequivocally reveal whether STDs really causemale infertility.Insummary,theremaywellbean associationofunknowngenesisandpossiblywithdifferent pathogenicmechanismsfordifferentpathogens. Alterna-tively, some STDs may cause male infertility, whereas others may not; however, there is hardly a strong correlation.Toreachmorefirmconclusionsonthesubject, higherqualitystudiesareneeded.

Authorcontributions:MikkelFodehadfullaccesstoallthedatainthe

study and takes responsibility for the integrity of the data and the

accuracy of the data analysis.

Study concept and design: Fode, Fusco, Lipshultz, Weidner.

Acquisition of data: Fode.

Analysis and interpretation of data: Fode, Fusco, Lipshultz, Weidner.

Drafting of the manuscript: Fode.

Critical revision of the manuscript for important intellectual content: Fode,

Fusco,Lipshultz,Weidner.

Statisticalanalysis:Fode.

Obtaining funding: None.

Administrative, technical, or material support: None.

Supervision: None.

Financial disclosures: Mikkel Fode certifies that all conflicts of interest,

including specific financial interests and relationships and affiliations

relevanttothesubjectmatterormaterialsdiscussedinthemanuscript

(eg,employment/affiliation,grantsorfunding,consultancies,honoraria,

stock ownership or options, expert testimony, royalties, or patents filed,

received, or pending), are the following: None.

Funding/Supportandroleofthesponsor:None.

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