Post-Infective IBS

Post-infective IBS is the name given to the condition suffered by a number of patients with Irritable Bowel Syndrome who report that they had normal bowel habits prior to a bout of gastroenteritis, diarrhea and/or vomiting.  Post-infective IBS without concurrent anxiety, depression or neurotic presentations has a relatively good prognosis and recovery is more rapid.

The most common causes of the gastroenteritis are viral, followed by Campylobacter, Salmonella and Shigella. Viral gastroenteritis typically heals rapidly with little residual damage to the gastrointestinal wall. However, bacterial gastroenteritis on the other hand can often produce ulceration and bleeding, and is more likely to be associated with with post-infective IBS.

Spiller studied 386 cases of bacterial gastroenteritis obtained from a community survey. The average duration of illness was seven days with a third of patients reporting bloody diarrhea and a median weight loss of 6kg.

Traveler’s diarrhea is extremely common in Australians travelling to Asia and Indonesia, as it is in Canadian citizens traveling to Mexico. In one study of Canadian travelers nearly 50% developed travelers diarrhea and the incidence of new IBS three months later was 17.5% compared with just 2.7% for those who did not get travelers diarrhea.

Post Infective IBS risk factors

Diarrhea and vomiting is a normal reaction to infection and helps to clear the gastrointestinal tract of infection. Most patients with bacterial gastroenteritis recover fully and only about 10% seem to develop post-infective IBS. The risk factors are:

• Being of the female sex,
• Hypochondriasis (although it could be argued that the "hypochondriasis" is the result of some predisposing weakness)
• Adverse life events in the previous year
• Duration of the initial illness is a very strong risk factor for post-infective IBS
• The specific infecting bacteria is likely to be important, since Spiller found around 10% of Campylobacter infected individuals developed post-infective IBS, compared to just 1% with Salmonella.
• The severity of tissue damage and ulceration may be major predictor.

post-infective IBS PATHOPHYSIOLOGY

Diarrhea related illnesses are characterized by faster Gastrointestinal transit time and increased gut sensitivity. This gradually returns to normal, but may do so at a variable rate. By three months, most of those who are going to recover will have done so and thereafter the rate of recovery is much slower.

Spiller and colleagues  performed longitudinal rectal biopsies in individuals recovering from Campylobacter gastroenteritis at 2, 6, 12 and 52 weeks, and noted initial increases in both inflammatory cells and enteroendocrine cells. Most returned towards normal, but in a few markedly symptomatic individuals the biopsies remained abnormal.

Similar abnormalities were noted in patients attending the outpatients with a history of post-infectious IBS. There is a good correlation between the inflammatory cells and the enteroendocrine cells, which Spiller interpreted as suggesting that cytokines might drive the enteroendocrine cell hyperplasia.

Other authors have noted increased enteroendocrine cells in unselected IBS patients but this needs confirmation. More important than increase in numbers may be the increase in release of 5HT. Several pilot studies have suggested that there was an exaggerated release of 5HT following a meal, particularly in those who got meal-related symptoms.

Treatment of post-infective IBS

It is important that patients understand the important roles of anxiety, stress and diet and persisting low-grade inflammation in this condition. Providing the Rome criteria are met and general physical examination is normal, then the probability of an alternative diagnosis is low. However, infections can unmask other disease, particularly celiac disease, inflammatory bowel disease such as Crohn's, and tropical sprue together with hypolactasia. Such patients should, therefore, undergo a minimum set of screening tests, including endomysial antibodies, hemoglobin, CRP, ESR, albumin and stool culture.

In the absence of alarm features such as weight loss, fever, rectal bleeding and nocturnal diarrhea, only 5% of all these tests are likely to be abnormal. Since microscopic colitis has also been reported to develop acutely after an infectious illness, it is important to do a colonic biopsy and, if suspicions are high, also a duodenal biopsy to exclude celiac disease.

Lactose intolerance developing after a viral gastroenteritis is well recognized by pediatricians. This occurs because lactase, the enzyme responsible for digesting lactose, is expressed fully only in the mature enterocyte at the tip of the villus.

Since viral gastroenteritis generally specifically damages the villi, lactase levels remain low for some months. A low lactose diet is, therefore, worth trying.

Since psychological factors are so important, it is necessary to make some formal assessment of the causes of the anxiety and depression. Where anxiety and depression levels are high, they should be treated on their own merits, since it is unlikely the patient will recover without addressing these psychological issues concurrently.