Bacterial and viral etiology of childhood diarrhea in Ouagadougou, Burkina Faso

Acute diarrheal disease is a major public health problem throughout the world, with over two million deaths occurring each year, and affecting mostly children under 5 years of age in developing countries [1, 2]. These diseases are especially common in developing countries with poor hygiene and sanitation and with limited access to safe drinking water. Underlying conditions, such as malnutrition, which increase the risk of contracting diarrhea, are also common in these countries. These factors may result in a significant disease burden and economic effect due to direct medical costs, loss of work, lower quality of life and mortality. The etiological agents for acute diarrhea include a wide range of viruses, bacteria and parasites. In Burkina Faso, diarrhea is the third most common cause of young children to visit a health care centre, but knowledge of its causative agents is limited. In our previous reports, rotavirus and diarrheagenic Escherichia coli (DEC) were found to be common causes of childhood diarrhea [3, 4]. Recently, two studies using conventional diagnostic techniques were conducted in Ouagadougou to determine the occurrence of certain viruses, bacteria and parasites in children with diarrhea [5, 6]. Yet, a comprehensive study on the actual significance of the etiological agents in acute diarrhea that also includes a control group of healthy individuals has not been performed. Here, we report on a one-year follow-up study using a combination of conventional and molecular methods to search for Salmonella spp., Shigella spp., Campylobacter spp., Yersinia spp. and the most common pathogroups of DEC including enteropathogenic E. coli (EPEC), enterotoxigenic E. coli (ETEC), Shiga toxin-producing E. coli (STEC), enteroinvasive E. coli (EIEC) and enteroaggregative E. coli (EAEC) as well as rotavirus and adenovirus in stool samples of children with and without diarrhea in urban Burkina Faso. In addition, seasonality of diarrhea, demographics and clinical features related to the pathogen-associated diarrhea were investigated. We also determined the serotypes and antimicrobial resistance patterns of the Salmonella and Shigella findings.

We used a combination of conventional and molecular diagnostic techniques to investigate the occurrence of bacterial and viral enteropathogens in stool samples of Burkinabe children with and without diarrhea living in an urban area.

The prevalence of diarrheal pathogens was significantly higher in patients (64%) than in control children (8%). Similar results have also been reported from other countries [10, 11], showing the importance of bacterial and viral infections as a cause of childhood diarrhea. In Ouagadougou, the prevalence of pathogens was higher in patients than was detected in the previous studies carried out in Burkina Faso [5, 6]. This is probably because, unlike the other reports, we investigated also the presence of different DEC pathogroups and Campylobacter, and these findings increased the frequency of detecting the causative agents of diarrhea. Rotavirus was the most frequently detected enteropathogen, supporting the well-documented role of rotavirus in childhood diarrheal disease in Burkina Faso as in some other developing countries [3, 5, 12–14]. A majority (90%) of the rotavirus infections occurred among children under 2 years of age. The occurrence of the other virus investigated in this study, adenovirus, was relatively low (5%) but somewhat higher than the 2% found in the previous study in Burkina Faso [6]. A comparable prevalence of 5% has been reported from both Tanzania and Tunisia [15, 16].

The various DECs investigated by multiplex PCR were the second most common group of enteropathogens detected in our study. Their prevalence (24%) was slightly lower than that (31%) found in our previous study in children living in the same urban area [4]. EAEC was the most commonly detected E. coli pathogroup in both patients and control children, suggesting that EAEC is actually not associated with diarrhea. Also other studies [17, 18] have reported similar results, whereas some studies have concluded that EAEC are causes of diarrhea [10, 11]. Our results together with the results from previous studies conducted in Nigeria and Ghana suggest that EAEC is endemic in West Africa [4, 19, 20], but is not a primary cause of diarrhea. The frequencies of EPEC (8%) and ETEC (4%) were lower than in our previous report (16% and 13%, respectively) [4]. However, that study was conducted during the rainy period, which may explain the differences. Nevertheless, these E. coli pathogroups can be considered as major bacterial causes of infantile diarrhea in developing countries [19, 21, 22].

In the present study, Salmonella enterica ssp. enterica comprising several serotypes was isolated from 9% of the patients. This percentage is high compared to the previous studies carried out in Burkina Faso (2%) [5] and in southeastern and eastern Africa, e.g. in Mozambique and Tanzania in which the prevalence was approximately 3% [23, 24]. Shigella spp. were isolated from 6% of the diarrheal children with a predominance for S. flexneri. Other researchers in Burkina Faso [5], in Tanzania [24] and in Jordan [25] reported similar rates for shigellosis. Our study was the first one to detect Campylobacter jejuni/coli in Burkina Faso; this pathogen is not searched for in the routine laboratory investigations for etiology of diarrhea. Our results show that Salmonella, Shigella and Campylobacter occur nearly exclusively in symptomatic children. A larger sample size is required however to confirm the statistical significance of this result.

Co-infections with two or more enteropathogens were common, making it more difficult to define the exact etiology of diarrhea and the exact cause behind symptomatic children. Moreover, parasites and other viral enteropathogens, such as norovirus and sapovirus, which were not included in our study, can cause enteric infections [14, 26] and may be responsible for illness in some of the 36% of cases with no etiologic diagnosis. In our study, the children in the control group were older than the children in the patient group. However, 76% of all pathogens were found in the patients aged 0–24 months, although all the pathogens in the control group were found in older children. This suggests that young children are susceptible to the enteropathogens, but with increasing age and living in the endemic area, they acquire some degree of resistance to enteric infections. When the association of the enteropathogens with the age of diarrheal children and their clinical features were examined, the most prevalent pathogens rotavirus and DEC were most common as sole pathogens in the youngest age group (0–12 months old children), whereas Salmonella and Shigella were mainly found as sole pathogens in children older than one year, as also reported by Nguyen et al. [27]. The occurrence of watery diarrhea was far more common than bloody diarrhea. Also, other symptoms were, in general, similar regardless of the detected pathogen, as has been reported before [25].

The antimicrobial susceptibility tests showed that only 20% of the Salmonella strains but 81% of the Shigella strains were resistant to trimethoprim-sulfamethoxazole, which is the most commonly used antimicrobial treatment for the Burkinabe children already previous to their enrollment in to the health center [5]. However, the resistance rates to the newer generation antimicrobials as detected in our study were still very low.

In conclusion, this study highlights the importance of the bacteria and viruses as the cause of diarrhea diseases in young children in Burkina Faso. Rotaviruses and E. coli pathogroups were the most common etiological agents in acute diarrhea during the one year study period. Seasonal variation was seen in the occurrence of the etiological agents. Constant antimicrobial surveillance is warranted to observe the potential emergence of the enteric bacteria resistant to the antimicrobials that are presently important in treatment of severe infections.