Diarrheal diseases have been described as far back as the ancient Greek civilization [1, 2]. For instance, Hippocrates’ writings (460–370 B.C.) were likely referring these diseases, describing them as “abundant liquid stool at short intervals” [3, 4]. During the Middle Ages, terms including Rheuma Gastros (running stomach) and Rheumatismus (stomach ache) used respectively by Gallien [5] and Alexandre de Tralles [6], focused on the physiopathological mechanism of the disease. In year 30, Celse revealed more clinical elements of the disease: «… the patient excretes blood which is usually mixed up with liquid excreta and at other times with mucus» and considered diarrhea as «an illness in which intestines are not to able to retain anything, and in which almost everything in the alimentary canal is lost as soon as it is eaten without digestion» [7]. Following Celse’s contribution, Gallien established inappropriate hygiene as the cause of diarrhea in his theory of “aqueous humour”, stating that toxic substances were present in the stomach and that diarrhea was a mechanism of evacuation. This remained as the primary etiologic theory for centuries. Towards the middle of the 17th century, Fernel classified diarrhea as an intestinal disease in the same category with intestinal blockages, gastric ulcers, and amebiasis. Like Gallien and Fernel, Grall et al. also subscribed to the view suggesting that poor food hygiene was the cause of diarrhea [8]. The first descriptions of diarrhea in developing countries date back to 1883 when Vibrio cholerae was isolated in Egypt during the third 1865 world cholera epidemic [9, 10]. It is this third great epidemic that left endemic hubs; some of which have endured to date. Unfortunately, a lack of information prevents an appreciation of the disease evolution since the discovery of the vibrion in Egypt until the middle of the 20th century. The first accurate data on the epidemiology of diarrhea date back to the 1960s. According to the WHO, a specialized team worked in seven developing countries from 1960 to 1965 and reported that the monthly prevalence rate among children less than 6 years of age was 40% [11]. Studies carried out in diverse regions of the world in order to appreciate accurately the magnitude and gravity of the problem led to the estimation that 500 million children had undergone one or more diarrhea episodes, and 4.6 million deaths had occurred from it in 1980 [12]. Thirty years later, estimates still report a high incidence and prevalence of diarrhea.

According to the World Health Organization, each year there are an estimated 4 billion cases of diarrhea. In 2007, 1.8 million people died worldwide from diarrheal diseases (including cholera), with 88% of these diarrheas being attributable to unsafe water supply, inadequate sanitation and hygiene. They were the second leading cause of disability-adjusted life years (DALY) lost and were the third leading cause of death (4% of all deaths) [13]. Presently, the risk of contracting diarrheal diseases are increased 5-fold in sub-Saharan Africa compared to developed countries (39.1% vs. 7.2%, respectively) [14]. Thus, diarrheas are an imminent threat to public health, particularly in the developing countries where it is one of the main causes of morbidity and mortality in children under 5 years of age (90%) [15]. In those countries, the average number of episodes of diarrhea per child per year within this age group is 3.2, and 21% of childhood mortality in children is associated with diarrhea, resulting in nearly two million deaths per year. In sub-Saharan Africa, mortality caused by acute diarrhea varies from 1.9% of all deaths in Gambia to 37% in Nigeria, with most of the deaths occurring during the first year of life [16–18]. Apart from well-described enteropathogens such Shigella spp., Salmonella spp., and enterotoxigenic such Esherichia coli, there are also a wide variety of viruses and protozoa that cause diarrhea in those endemic areas. Although diarrhea are recognized as a serious public health problem in Cameroon, no comprehensive studies relating diarrhea-causing pathogens responsible for endemic diarrhea among Cameroon’s children have been reported in the medical literature. The aim of this study is to describe the main etiologic infectious agents of diarrhea in Yaoundé and their distribution within the urban space.

Epidemiologic features: A total of 3,034 children aged up to five years were enrolled in the study. Among these, diarrhea was one of the diagnoses in 437 (14.4%) (Table 1).

Samples were collected from all of them (100%). Seventy two (16.47%) were younger than 12 months of age, and two hundred ninety eight (68.19%) were between 12 and 36 months of age (Table 2).

Co-infections were found in one hundred and twenty five children, accounting for 48.1% of the total number of positive cultures. Of these positive samples, four (3.2%) were virus/parasite co-infections, one hundred and five (84%) were bacteria/parasite, and sixteen (12.8%) were virus/bacteria/parasite co-infections. Three hundred fifty eight (81.9%) children were males, i.e. a male-to-female ratio of 1:4.5. One hundred ninety nine parents (45.5%) were thinking of seeking medical attention (hospital) for their sick children, whereas ninety five (21.7%) were thinking of resorting to street pharmacists (street medicines dealers), eighty six (19.6%) to traditional remedies, and fifty seven (13.1%) did not have any therapeutic choice. Low level of diarrhea (Fifty six, 21.5%) was identified in formal i.e. planned settlement, whereas high level of diarrhea (two hundreds and four, 78.4%) was found in children living in unplanned settlement, namely in central and sub-central spontaneous neighbourhoods (Figure 3).

Etiologic agents: On the 437 samples examined, a potential infectious pathogen was isolated from 260 (59.5%). Pathogenic viruses were isolated from 10 (3.8%) samples, bacteria from 96 (36.9%), and parasites from 106 (59.2%) (Table 3).

Those pathogens were unequally found among the children. Enteric adenovirus (02.7%), Salmonella spp. (09.6), Campylobacter spp. (08.8%), Esherichia coli - enteropathogenic (04.2%), Shigella spp. (07.3%), Ascaris lumbricoides (17.8%), Giardia lamblia (13.2%), Trichuris Trichiura (10.7%), and Entamoeba (08.4%) were the most frequently found pathogens (Table 4). Rotavirus was found in only three children, all younger than 23 months. The presence of Salmonella spp. (P < 0.005) or Campylobacter Jejuni (P < 0.003) was statistically related to age, being more frequent among children between 12 and 35 months of age; whereas Ascaris Lumbricoides (P < 0.001) and Trichuris trichiura (P < 0.003) were more frequent in children between 12–59 months of age. Though not significant, Shistosoma intercalatum was the very rare pathogen to be isolated.

Clinical features: In all children having had a microorganism isolated or not, fever and cough were the most recurrent clinical finding, whereas vomit and pains were frequently found only among children with Ascaris lumbricoides, Giardia lamblia, and E. coli (EPEC, EAEC). Persistent diarrhea i.e. diarrhea that continued for longer than 14 days occurred in 14.41% (63 of 437). These sixty three children were between 6 and 23 months of age and were infected with two or three pathogens. Analysis of fecal samples in children with diarrhea showed watery diarrhea in 72.3%, diarrhea with mucus in 20%, diarrhea with blood in 3.1% and diarrhea with mucus and blood in 1.6 % of all patients. From the two hundred and sixty children with infectious diarrhea, two hundred and two children (77.7%) were diagnosed with malaria. Only ninety seven (22.2%) children were well-nourished. Whereas sixty nine (15.8%) had severe malnutrition, one hundred and one (43.7%) had moderate malnutrition, and eighty (18.3%) had mild malnutrition. Other Clinical features included symptoms of upper respiratory tract infection (21.9%), and abdominal pain (12.5%).

This study, which covered a 3-months period, was the first direct field investigation in Cameroon of pathogenic agents associated with diarrhea in children. The results found in the present study are in whole similar to those reported from other countries where diarrheal diseases are recognized as a major cause of morbidity and mortality in children under five years of age [35]. Our male-to-female ratio of 1:4.5 is close to that of several studies which reported higher number of male patients as compared to female patients to have suffered from diarrhea [36–38]. In this study, at least one pathogenic microorganism was isolated from 59.5% (260/437) of the stools of children with diarrhea. In spite of Mandomando and Sur [23–39] who reported a low rate (42.2%), this percentage is similar to previous studies carried out and which well correspond with health realities in developing countries [40–42].

It is difficult to draw conclusions about rotavirus because of the low rate of detection of this virus. However, this result is not surprising because usually during the rainy season, percentages of diarrhea due to rotavirus are lower than during the dry season [43, 44]. On the other hand, rotavirus has been associated with approximately one quarter of all diarrhea in South Africa [45]. Group A rotavirus is the most common human strain, with a worldwide distribution, whereas Groups B and C are mainly found in East and South-East Asia [46, 47]. No data on the prevalence of the different groups are not available for Cameroon. An explanation would be that cases of rotavirus either were not severe to cause diarrhea or had short duration. Thus, there’s a need for longer studies with adequate methodology in order to determine the real rotavirus prevalence in Cameroon. However, Enteric adenovirus has displayed a high prevalence compared with rotavirus. This can be due to their epidemiologic feature: notwithstanding the types, all are transmitted by direct contact, fecal-oral transmission, and occasionally waterborne transmission. Some types are capable of establishing persistent asymptomatic infections in intestines of infected hosts and infections can occur throughout the year [48]. Case of Enteric adenoviruses serotypes 40 and 41 that we isolated, mainly in stools of children between 5 and 12 months of age (57.14%).

Despite Gascon and Lindblom [49, 50] who described a low percentage of Campylobacter jejuni isolated in children, our results show a different pattern - probably because our study design has included children from one to five years, an age strata at which Campylobacter is more prevalent. The relatively lower frequency of Salmonella spp. found in our study is consistent with that of African studies in which they were isolated in less than 10% of children younger than five years of age with diarrhea [51, 52]. These salmonella are likely to adapt to domesticated cattle and all varieties of fowls and chickens. The reservoir of infection in animals constitutes the principal source of diarrhea caused by Salmonella spp. Shigella spp. has also been enteropathogens statistically related with an increased risk of diarrhea in under five years children in Yaoundé. Asymptomatic infection was common and may have arisen due to prolonged excretion of organisms [53]. Its relatively low prevalence in our study may be explained by the fact that it included severe cases requiring hospitalization. Yet, we did not investigate hospitalized children. Furthermore, Shigella spp. usually appears in outbreaks, so that in the absence of an epidemic, it is not frequently isolated [54].

As well as other enteropathogens, Diarrheagenic E. coli were frequently isolated, supporting the well-documented role of this sp. in diarrheal disease [55, 56]. The main E. coli pathotype found was Enteropathogenic Escherichia coli (EPEC, 04.2%). The picture is similar to a study in Argentina, where EPEC was isolated from nine cases (04.5%) of a total of 200 diarrhea patients [57]. EPEC is a well known enteropathogen. Together with Enterotoxigenic Escherichia coli (ETEC), they cause an important number of cases of diarrheal illnesses with dehydration [58]. However, in some studies, ETEC and EPEC strains were not related to diarrheal illnesses [59, 60] As far as Enteroaggregative Escherichia coli (EAEC) strains, they were first described as a putative virulence group by Nataro et al. [61]. In our study as well as in others [62, 63], EAEC was not related to diarrhea. This might be so because hosts factors like vertically acquired antibodies or breast milk could have played a role in the pathogenesis of diarrhea whether acute or persistent [64]. Another hypothesis might be an unexpectedly long period of EAEC strain excretion in feces after a diarrhea episode treated with only rehydration salt and exceeding the two weeks without diarrhea required for controls [65]. The low frequency of verotoxin-producing E. coli (VTEC, 01.5%) reported in our study is consistent with others studies in low and middle income countries [66]. In those countries, prevalence of VTEC in childhood diarrhea is lower than that of ETEC, EPEC, or EAEC.

Intestinal nematodes seem to play a great role in diarrheal diseases in this area. The high rate of parasites isolated from stools samples suggests a high prevalence and even incidence of these health problems in the Yaoundé urban and rural region for children at this age. The epidemiologic data suggest that there is an age dependency in the isolation or parasites, especially in the case of Ascaris lumbricoides and Trichuris trichiura, both being more frequently isolated in children older than twelve months, and statistically related to diarrhea. This could be because, children older than twelve months of age are in permanent contact with soil and thus more prone to infection, and have non hygienic feeding habits. In short and as reported in Venezuelan and Brazilian children [67, 68], the high and statistically significant frequency of enteric parasites in our study is conclusive of their role in diarrheal diseases. Also, the fact that Entamoeba histolytica, Giradia lamblia, and Trichomonas intestinalis are a cause of diarrhea here is a well-documented fact [69].

Another observation from the present study is that infection with multiple pathogens was very common. This is the reflection of environmental contamination [70–72], but it makes it difficult to identify which pathogen is the real causative agent of an episode of diarrhea. It might also be that multiple microorganisms act synergistically to produce diarrhea. The presence of fever in most diarrheic children could be caused by malaria, as the disease is endemic in the area and that nearly 77.70% of the children were positive with Plasmodium falciparum parasites. Vomiting was frequent in children with Giardia lamblia, Ascaris lumbricoides, Enteric Adenovirus, and E. coli. Blood noticed in the stools might be caused by Shigella spp. as its capacity to penetrate and multiply within the intestinal mucosa, causing ulceration is well known [73].

Despite the recognition of severe ill effects of the disease and mostly the enormous amount of resource being spent to control their spread [74], diarrhea still remains a serious threaten in many urban communities for a number of reasons: high incidence of malnutrition and infections, overcrowding of children in one house, lack of personal hygiene, lack of piped water and sanitation, widespread faecal contamination of the environment, and poor quality of housing [75–77]. In Yaoundé, this is particular obvious in informal settlement namely in central/sub-central and Peri urban neighbourhoods’ with poorest living conditions and consequently with a higher level of diarrhea (≥78%). However, formal settlements such as wealthy residential neighbourhoods and housing estates provided with all the urban utilities and infrastructure [78] display a lower level of diarrheas. This finding that levels of diarrhea diseases vary from one neighbourhood to another within the urban space might be a reflection of changing patterns of urban settlement.

Diarrheal diseases are one of the main health problems in Cameroon, as in many low-and-middle income countries. Clarification of the microorganisms associated with diarrhea in Cameroon is an essential step toward the implementation of effective primary health care activities against the disease. The present etiological study is also meaningful in that it provides information on the prevalence of enteropathogens in various neighbourhoods. Thus, this study opens door to further investigations aiming at analyzing specific epidemiology and virulence of diarrhea-causing pathogens in Cameroon. Therefore, suitable and efficient local control strategies can be set up. From a methodological point of view, analysis of diarrhea-causing pathogens according to neighbourhoods is a proof that a spatial epidemiological study at urban districts scale can be relevant in developing urban settings as whole. Such study is urgently required to disaggregate urban health information into smaller and manageable districts so as to guide local decision making on urban health. The contextual level of analysis allows showing that levels of diarrhea differ across the city. For example, Figure 3 shows that diarrheal prevalence varies across the city neighbourhoods. From these intra-urban variations, the learning objective is that, contrary to the existing literature on African urban environments, all the poor are seldom at the same risks in an urban neighbourhood. In health planning, such knowledge can be useful for setting suitable and effective strategies disease and health intervention strategies that are able to adequately address neighbourhood health determinants.