Chapter 7c FOOD POISONING/BACTERIAL INFECTIONS OF THE GUT

Chapter 7c

FOOD POISONING/BACTERIAL INFECTIONS OF THE GUT

1. OVERVIEW

Gastrointestinal infections are rampant throughout the world, developed as well as undeveloped. For example, it is estimated that more than 200 million episodes of acute gastrointestinal infection occur annually in the U.S.

originating in contaminated food in 76 million, from water in 13 million and 122 million from human to human transmission (1). Infections of the gut are caused by a multitude of organisms from viruses to protozoa but the bacteria responsible are generally gram negative organisms. Whatever the organism they are most often transmitted by infected food or water or directly from another human. Presenting a variety of symptoms complexes they are typically associated with diarrhoea and possible systemic symptoms and are often brief. The subject is a vast one and the reader is referred to specialised texts (1, 2).

The organisms responsible separate into two categories:

1. TOXIGENIC The toxins produced are of two types, either cytotonic which stimulates intracellular energy processes, or cytotoxic which produces damage to the intestinal mucosal cells. These organisms mainly affect the upper gut, do not invade the mucosa but attach themselves to it producing toxins which alter the function of the mucosal cell, often activating the adenylate cyclase system so that there is an outpouring of fluid into the gut producing watery diarrhoea without blood or mucus. Typical ones are:

• V. Cholerae and enterotoxigenic E coli (ETEC) which produce a

toxin leading to diarrhoea and dehydration from failure of

82 Chapter 2 7c absorption of salt and water and a concurrent excessive secretion

of fluid in the upper gut from cells which appear normal.

• Other toxigenic types of coliforms described are enteropathogens, enteroinvasive, enterohaemorrhagic and enteroaggregative.

2. INVASIVE. These mainly affect the terminal ileum and colon and produce ulceration of the mucosa and cellular invasion, characteristically producing a bloody mucoid diarrhoea, rectal pain, fever and systemic symptoms and sometimes blood stream invasion. The major types are:

• SHIGELLA

• SALMONELLA

• CAMPYLOBACTER

• YERSINIA

• VIRAL DIARRHOEA

• ENTEROINVASIVE E Coli

Although the pathogenic organisms show common symptoms such as diarrhoea, there are features peculiar to organisms and their ecology which help to distinguish them.

• SHIGELLA organisms characteristically produce dysentery, that is diarrhoea with blood and pus of acute onset, rectal pain and fever and systemic symptoms with abdominal pain. The disease is associated with disruption and poor hygiene and is common in war situations accounting for about 10-20% of diarrhoea around the world. It is transmitted by the faecal-oral route, relatively few organisms are necessary to create disease and, strangely, 1 in 4 volunteers fed the organism do not develop the disease. It is mostly seen in children from six months to five years.

Shigella organisms produce one of the most contagious forms of GI infection. The only natural host is man, like Salmonella typhi and i spread from man to man, or more often child to child. The infective dose is low, so that the disease spreads rapidly, not only in families but in institutions and day care centres.

• SALMONELLA infections are widespread, increasing and transmitted by the five Fs “flies, food, fingers, faeces and fomites”. The organisms are widespread in nature inhabiting animals from sheep to fleas but particularly poultry; food contaminated in preparation is important in transmission. One of this genus, salmonella typhi produces typhoid fever which is rather different in many respects. Several syndromes are seen but the most frequent is diarrhoea lasting several days, preceded by nausea and vomiting. Salmonella organisms, particularly S.typhi tend to invade the blood stream and may localise in various organs.

• On the other hand there are HALOPHILIC BACTERIA such as V.

parahaemolyticus which live in seawater and which can be transmitted

by infected shellfish.

FOOD POISONING/BACTERIAL INFECTIONS OF THE GUT 83

• CAMPYLOBACTER are generally transmitted from poultry, meat, dairy products and water and mostly occur in sporadic cases. Massive outbreaks are unusual, partly because it does not replicate in food and is not very contagious. It is, in western societies, now the major bacterial cause of gastroenteritis.

• YERSINIA enterocolitis causes a variety of syndromes from acute gastroenteritis to an invasive enterocolitis predominantly effecting children. It is most often reported from Northern Europe and Scandinavia. Widespread in animals it may enter the blood stream when immunity is compromised.

• VIRAL DIARRHOEA is a major cause gastroenteritis in the world being responsible to 30-40% of cases. The pathogens fit into four classes:

•ROTAVIRUS This is responsible for about one third of hospitalised S gastroenteritis in childhood, principally affecting infants of three to fifteen months of age.

•CALICIVIRUS These are especially seen in day care centres; major S representatives are the Norwalk and Norwalk-like viruses. These occur in all ages except infants. Shellfish are a frequent source as is the faecal-oral route but typically it causes explosive outbreaks in nursing homes, cruise ships, schools and military camps.

•ENTERIC ADENOVIRUS This is generally a nosocomial infection. S

•ASTROVIRUS This is an organism of low infectivity, infecting children S aged less than six months and often occurring in day care centres.

Three protozoa require mention:

• CRYPTOSPORIDIA These unicellular organisms are generally conveyed in drinking water from which it is difficult to eradicate them but its transmission, especially from infected children, readily takes place e.g.

in children in day care centres and schools.

• GIARDIA In the west this is especially seen in children in day care centres where it is readily spread not only to other children but to adults, especially young women. It is also seen in homosexual men.

• ENTAMOEBA HISTOLYTICA This is largely a water borne infection, following faecal contamination.

References

1. Musher DM, Musher DL. Contagious acute gastrointestinal infection. N. Engl. J. Med.

351,2417-27 (2004).

2. Hamer DL, Gorbach SL. Infectious diarrhoea and bacterial food poisoning In : Feldman

M, Friedman LS, Sleisinger MH eds. Sleisinger and Fordtran’s Gastrointestinal and

Liver Disease. Pathophysiology / Diagnosis / Management. 7

Edn. (W B Saunders,

Philadelphia, 2002).