The principal aims of this study were to compare the frequency of atypical EPEC with frequencies of established enteropathogens in children attending hospital with diarrhea and to determine the clinical and laboratory features associated with each pathogen. During the first part of the study (when pathogenic E. coli
was sought), atypical EPEC was the predominant pathogen identified; it was found in 31% of 134 children compared with 10% for adenovirus, 10% for Salmonella
sp., 9% for Campylobacter
sp., and 4% for rotavirus. In the second period of the study, when EPEC was not sought, rotavirus predominated. In agreement with our findings from a community-based study in Melbourne and reports from investigators in Brazil, Norway, and elsewhere (9
), the atypical EPEC strains obtained in this study were highly heterogeneous in terms of O:H serotype and intimin type, which indicates that the high frequency of atypical EPEC was not due to an outbreak caused by a limited number of strains. Also in agreement with our previous study, we observed that serotypes of EPEC associated with diarrhea differed from those listed by the World Health Organization as being characteristic of EPEC (9
To determine whether atypical EPEC is a cause of diarrhea, we compared the clinical and laboratory findings of children who were infected with these bacteria with those who were infected with well-established pathogens and those in whom no pathogens were identified. The hypothesis underlying this investigation was that if atypical EPEC is not a pathogen, the symptoms, signs, and laboratory findings in patients infected with these bacteria would be the same as those in patients in whom no pathogens were found. The results showed that diarrhea attributable to atypical EPEC was significantly more common in boys and that it persisted significantly longer than diarrhea in patients without an identifiable pathogen or in those infected with adenovirus, rotavirus, Campylobacter spp., or Salmonella sp. This study also showed that infection with atypical EPEC generally occurred in children <2 years of age, with 72% <24 months of age compared with 55% for the first study group as a whole (OR 3.0, 95% CI 1.17–7.85, p = 0.03, 2-tailed Fisher exact test). Infection with EPEC was associated with vomiting in ≈50% of patients, was generally not accompanied by fever, abdominal pain, or dehydration, and was not characterized by fecal blood or leukocytes, indicating that it was not inflammatory in nature. The reason for the higher frequency of atypical EPEC in boys is not known but confirms our unpublished observations from a community-based study, in which 55 isolates were obtained from 338 male patients, and 34 were obtained from 358 female patients (OR 1.85, 95% CI 1.17–2.92, p = 0.009, 2-tailed Fisher exact test).
The validity of the clinical and laboratory assessments performed in this study was indicated by the confirmation of the well-known associations of specific pathogens with particular parameters: younger age of children infected with EPEC and viruses than those infected with Campylobacter
spp.; rotavirus and Salmonella
infections with fever; rotavirus with dehydration and an overall greater severity of disease; Campylobacter
sp. with fecal blood; and Campylobacter
spp. with fecal leukocytes (22
Persistent diarrhea (lasting more then 14 days) eventually develops in a substantial proportion of children with acute infectious gastroenteritis and may become chronic, leading to malabsorption, failure to thrive, and malnutrition (23
). A wide range of infectious agents has been implicated in the cause of persistent diarrhea, including viruses, in particular rotavirus; protozoa, such as Giardia
spp., and bacteria, including E. coli
). In most cases, however, laboratory investigation of children with persistent diarrhea fails to yield an identifiable cause. The findings of this study suggest that a number of these cases may be caused by infection with atypical EPEC, which is seldom sought in these patients.
Despite the persuasive evidence of a volunteer study and reports of outbreaks of diarrhea attributed to atypical EPEC (25
), the role of atypical EPEC in disease is controversial. In several reports, however, from countries as diverse as Iran, Norway, Peru, Poland, South Africa, the United States, and the United Kingdom (20
), as well as Australia (9
), atypical EPEC strains have been identified in children with acute diarrheal disease. Atypical EPEC has also previously been reported in association with prolonged diarrhea (34
). For example, Hill et al. (35
) reported that of 26 children infected with EPEC requiring hospital admission for acute diarrhea, life-threatening, chronic symptoms developed in 6 (23%). Five of these 6 children were infected with EPEC of serogroups O114 or O128, which frequently do not produce Bfp (14
). Notwithstanding these previous reports, however, the current study is the first to characterize the illness caused by atypical EPEC in a systematic way and to compare the features of atypical EPEC infection with those of other etiologic agents of diarrhea.
The reasons why persistent diarrhea develops more frequently in children infected with atypical EPEC than in those infected with adenovirus, rotavirus, Campylobacter
spp. are not known. In a recent study, Mellmann et al. (37
) found that only 12 (<9%) of 137 patients who were infected with eae
-positive EHEC strains when investigated within 14 days of the onset of diarrhea remained culture-positive when retested 3–16 days later, compared with all 5 patients who were initially infected with eae
-negative E. coli
(i.e., atypical EPEC) (OR 110.4, 95% CI 5.8–2117.6, p<0.0001, 2-tailed Fisher exact test). These findings indicate that atypical EPEC may have an innate propensity to persist longer in the intestine than varieties of E. coli
which cause diarrhea that is more transient in nature. EPEC adheres tightly to epithelial cells and disrupts normal cellular processes (38
), and evidence suggests that atypical EPEC may retard apoptosis of intestinal epithelial cells (39
), possibly because of the lack of Bfp (40
). These features may favor prolonged intestinal colonization by atypical EPEC compared with other intestinal pathogens. Although disease due to atypical EPEC was mild and generally not associated with dehydration, its importance lies in its association with prolonged diarrhea, a major contributor to childhood illness, especially in developing countries. Our findings also suggest that interventions targeted towards atypical EPEC may be beneficial in managing children with prolonged diarrhea.