This study on diarrheal disease in Gabonese children is the first to assess the etiology of diarrheal syndromes in Koula-Moutou, Gabon. While data on adults and children already exist, children under 5 years old with diarrheal syndromes living in the semi-urban environment of the city of Koula-Moutou have not been previously studied.
In this study, the prevalence of children aged up to 5 years with diarrhea was 77.3%, it is similar to that reported by a previous study in another city in Gabon (21). The results of our study also showed that 41.6% of the children with diarrhea were aged 0 to 24 months old and were the most affected age group with a prevalence of 44%. Our results corroborate those of several studies led in Africa, with a higher prevalence found in children aged 0 to 12 months (8, 16, 22, 23). This predominance could be explained by the fact that generally, between 6 to 23 months of age, children are more vulnerable compared to those aged over 36 months old (24). Indeed, pathologies such as diarrhea are recurrent in this age group due to the gradual decline in maternal antibodies as well as the introduction of new dietary practices sometimes correlated with poor hygienic practices (24, 25).
A range of different pathogenic organisms can cause pediatric diarrhea in the world, especially in tropical and developing countries, including rotaviruses and adenoviruses (26), intestinal parasites such as Giardia intestinalis, Entamoeba histolytica (27), and bacteria such as Escherichia coli, Shigella spp, Salmonella, Campylobacter spp (8). This study shows a strong heterogeneity of parasites and bacteria in diarrheal cases in which most of the species are not isolated in control cases. The most common parasitic species isolated in diarrheal cases were Entamoeba spp, Ascaris lumbricoides, Blastocystis hominis, Ancylostoma duodenale, Giardia intestinalis, Endolimax nanus, Schistosoma spp and Trichuris trichiura. This profile is similar to that reported in previous studies (28, 29). In addition, Ascaris lumbricoides, Blastocystis hominis, Giardia intestinalis, Entamoeba spp and Trichuris trichiura appear to be the intestinal parasites most frequently involved in parasitic infections in Gabon (20). These species have a worldwide distribution and are characteristic of some countries (30). Regarding the bacterial group, 11 genera belonging to the Enterobacteriacea family were recorded, a similar profile was found in the work of Mbuthia et al. in Kenya. The diversity was specific to the Enterobacteriaceae, Pseudomonaceae and Vibrionaceae families (2). This bacterial diversity was marked by a clear predominance of Escherichia coli strains with an isolation rate of 26.6%, which is similar to other studies with variable frequencies (25, 31, 32). Likewise, this study isolated a high rate of bacteria less commonly incriminated for causes of diarrhea and belonging to the Raoultella, Serratia, Klebsiella, Enterobacter, Citrobacter and Pantoea genera (31.1%). Previous studies reveal that some of these strains, such as the Citrobacter spp and Klebsiella spp species, have acquired specific virulence genes, which can induce diarrhea and / or hemorrhagic colitis (2, 33).
Pathogen infection was significantly more prevalent in patients with diarrhea, with a prevalence of 46.1% compared to controls (10.0%). These results are similar to those reported by other studies (34, 35). On the other hand, this overall prevalence of pathogens recorded in diarrheal cases in this study was lower than those obtained by Okon et al. in Nigeria and Knee et al. in Mozambique who found prevalence rates of 61.8% and 86%, respectively (23, 32). This contrast could probably be related to the lack of characterization of diarrheagenic Escherichia coli (DEC) in this study. Furthermore, this study also shown the presence of parasitic pathogens in this population, with a frequency of 20.6%. This prevalence was, however, lower than that recorded in Nigeria (37.1%) (32), Cameroon (59.2%) (7) and Gabon (61.0%) (21). The high prevalence of infections due to bacterial pathogens in these conditions is similar to that found in other studies (8, 23).
One of the particularities of this study was the lack of bacterial pathogens isolated from controls. The frequency of bacterial infections (25.5%) is higher than that reported in a previous study by Koko et al. carried out in Libreville (17) who obtained a prevalence of 12.9%. This variability in epidemiological characteristics could undoubtedly be linked to the level of urbanization of the two zones, the environmental conditions and hygiene of the respective populations, which are all factors that influence the etiology of diarrheal diseases (9, 36). Salmonella spp strains were the most predominant in the bacterial profile of this study and accounted for 29.4%. This prevalence is in contrast with the one obtained in previous studies concerning developing countries, and particularly countries in the African region where the prevalence was markedly lower (37, 38). However, these data corroborate the work of Koko et al. in Gabon (17) and Rathaur et al. in India (39). Indeed, these studies identified Salmonella spp as a major etiological agent responsible for diarrhea. In addition, its presence could be correlated with domestic animals like poultry, which could constitute reservoirs of infection and a potential source of Salmonella diarrhea (7). The prevalence rates of the Shigella and Yersinia strains observed in this study, 4.9% and 2.0% respectively, can be explained by the epidemiological heterogeneity of the geographical areas (32, 37, 40, 41).
In this research, multiple infections of enteric pathogens were more found in diarrheal cases than in controls. This has also been reported in other studies particularly in patients with low or average income (35, 42). These results would suggest that more than one pathogen was responsible for the diarrheal disease in children living in Koula-Moutou. The presence of mixed infections complicates the diagnosis of a specific pathogen responsible for the disease and may result in an additive effect, which may lead to new clinical profiles (42). A reliable basic diagnosis must be established for better patient care and treatment.
Factorial correspondence analysis (CFA) reveals a predominance of parasites, Salmonella and Shigella in children over 12 months old. The parasitic data from this study are comparable to the literature which highlights an increase in parasitic infections in subjects over 12 months of age, for which the most likely explanation would be frequent contact with soil (7, 43). Likewise, this distribution of bacterial strains has already been reported by other authors (17, 23, 39).
The transmission and spread of diarrheal diseases are closely linked to environmental factors but also to living conditions, personal hygiene, behavior and domestic environment (44). In this study, univariate analysis of the data showed that the presence of rivers and domestic animals were the risk factors significantly associated with the occurrence of diarrhea in the town of Koula-Moutou. These results are consistent with the data reported by Bouba Djourdebbé et al. (24). Watercourses create a habitat conducive to the proliferation of microorganisms. Combined with other parameters, such as the proximity of animals which are potential pathogen reservoirs and the lack of knowledge on good hygiene practices, the presence of rivers influences the risk of contamination (24, 45). Given that diarrheal diseases can be linked to the presence of feces in water, the population of Koula-Moutou can be highly exposed to this health risk. Indeed, this city has a very dense water network which unfortunately serves for domestic use but in which wastewater containing the feces of some animals or even humans can be thrown away. These practices can obviously contribute to the fairly high prevalence of diarrheal diseases in this area.
This study has some limitations. It used only microbiological analyzes, including stool bacterial cultures, as they are the most common diagnostic routine methods used in developing countries. Stool culture may have a lower sensitivity of detection of bacterial pathogens than PCR, which allows the discrimination of different pathotypes and a better appreciation of the involvement of multiple infections with enteric pathogens associated with diarrhea (42). Moreover, the low proportion of controls in this study may not be representative of the correlation between enteric pathogens and acute diarrhea.