Background
Infectious diarrhoea is a significant cause of illness and death among children under 5 years of age in low-resource countries. It accounts for 9% of all deaths globally in this age group, and ranks only second to pneumonia [
1]. The majority of these cases are associated with the first two years of life, with peak ages being between 6 and 11 months [
1,
2]. Although mortality associated with diarrhoea has been decreasing since 2000, mainly due to the implementation of effective control programmes and improved socioeconomic status, it still remains an important reason for hospital admissions and deaths among the children [
3]. South-East Asia and sub-Saharan Africa bear the highest burden of the disease [
1,
4].
Interventions that target the main causes of diarrhoea should focus on the most susceptible children, and this should further accelerate decline of diarrhoeal cases. Guiding these efforts requires identification of aetiological agents and understanding the risk factors associated with diarrhoea. Most cases of diarrhoea are associated with consumption of contaminated water and food, and poor sanitation, which create an ideal environment for diarrhoeal pathogens to be easily transmitted [
2,
5]. Several pathogens have been implicated as important causes of diarrhoea, and these include a variety of bacteria, parasites and viruses [
4,
6,
7].
Although the most effective treatment for acute diarrhoea is fluid and electrolyte replacement, antibacterial agents are often indicated in dysentery, typhoid fever and severe cholera [
3,
8]. However, in recent years there has been growing concern of antimicrobial resistance in bacterial pathogens associated with diarrhoea [
9‐
11]. Thus, there is an urgent need for global surveillance of antimicrobial resistance as this is important in the management of children with diarrhoea [
12].
Despite diarrhoea in children being acknowledged as a serious public health problem in Zambia, there is a paucity of data on infectious diarrhoeal agents, especially bacterial pathogens and their antimicrobial susceptibility patterns due to the few studies that have been conducted in the country [
13‐
15]. Since aetiological agents and drug resistance patterns vary greatly across countries, regions and communities over time, current local knowledge of these patterns is essential to inform treatment, prevention and control programmes. Therefore, the aim of this study was to identify bacterial pathogens in stool samples obtained from children aged 0–59 months admitted with diarrhea to the University Teaching Hospital (UTH) in Lusaka, Zambia.
Discussion
Five different bacterial enteropathogens were isolated from some of the stool specimens, and these included
V. cholerae 01 Ogawa serotype,
Salmonella species,
Shigella species, DEC and
Campylobacter species.
V. cholerae was the most predominant pathogen due to a cholera outbreak during the study period. Our results were in agreement with previous studies done in Lusaka [
19,
20]. However, none of these studies focused on cholera in children.
Salmonella species was the second most prevalent genera (25.5%); and the majority of the species were S. Typhi followed by NTS and
S. Paratyphi B, which agrees with other studies conducted in India and Bangladesh [
21‐
23].
Among the DEC isolates, four strains were identified: ETEC, EIEC, EAEC and EPEC, with EPEC being the most predominant species. Four strains of DEC (ETEC, EIAC, EAEC and EPEC) were the third most common group of enteropathogens, accounting for 18.0% of all isolates. The predominance of ETEC strain, among the DEC, in agreement with previous studies carried out in Bangladesh, Tunisia and Kenya [
24‐
26]. ETEC was associated with one third of diarrhoea cases identified in children in the recent GEMS Study [
4].
DEC isolates were mainly recovered from children below the age of 24 months, which corroborates with the findings of a Nigerian study that also indicated that most of the DEC isolates were mostly recovered from this age group [
27]. In this study, EAEC was detected from only 3 specimens, and EIEC and EPEC strains were also detected but in low numbers.
Shigella species ranked third, with the most predominant species being
S. flexneri, and affected mainly children above 36 months of age. This finding was in conformity with previous studies that have implicated
S. flexneri as the dominant species [
28,
29]. However, other studies have indicated that
S. dysenteriae and
S. boydii to be more frequently isolated species [
28‐
30].
Only three
Campylobacter species were recovered from the children, which might probably be due to the fact that
Campylobacter is as a fastidious organism which requires special conditions for growth [
31]. However, in a community-based study on the pathogen-specific burden of diarrhoea in low-income countries, that involved eight study sites in South America, Africa and Asia,
Campylobacter exhibited the highest attributable burden of diarrhoea amongst infants aged between 0 and 11 months [
31].
In this study, all the organisms isolated exhibited high level drug resistance, including resistance to multiple drugs.
V. cholerae isolates were totally resistant to cotrimoxazole and nalidixic acid, partially resistant to erythromycin, ciprofloxacin and norfloxacin. A previous study in Zambia, during the 1990–1991 major cholera outbreak, showed resistant to cotrimoxazole (97%), tetracycline (95%), chloramphenicol (98%) and doxycycline (70%) [
19]. A similar study in Mozambique, found that the
V. cholerae O1 Ogawa isolates were resistant to cotrimoxazole (100%), ampicillin (100%), nalidixic acid [
9], chloramphenicol (97%), nitrofurantoin (95%), tetracycline (82%), azithromycin (56%) but sensitive to ciprofloxacin (100%) (101).
For the
Salmonella species, both
S. Typhi and
S. Paratyphi B were totally resistant to ampicillin, cotrimoxazole and streptomycin. In addition to the three drugs,
S. Typhi and
S. Paratyphi B were also significantly resistant to chloramphenicol and spectinomycin, respectively. These findings are consistent with other studies in which it was noted that there was an increase in the number of
Salmonella isolates being resistant to ampicillin, chloramphenicol and cotrimoxazole [
32].
A study on the Malawi-Mozambique border reported findings similar to those in this study in which 100% of
S. Typhi were resistant to ampicillin, chloramphenicol and cotrimoxazole [
33]. Another study carried out in Uganda showed that 76% of
S. Typhi isolates were resistant to ampicillin, streptomycin, sulfisoxazole, tetracycline, and cotrimoxazole, but were susceptible to chloramphenicol. This was in conformity with findings from this study which also found that all the
S. Typhi isolates were susceptible to ceftaxime, gentamicin, and spectinomycin [
34].
This study also demonstrated the occurrence of MDR strains of
S. Typhi,
S. Paratyphi B and the NTS which were resistant to all traditional first line drugs tested: ampicillin, chloramphenicol and cotrimoxazole. The commonest resistance pattern observed in this study was ampicillin-chloramphenicol-cotrimoxazole-streptomycin for
S. Typhi, ampicillin-chloramphenicol-spectinomycin-cotrimoxazole- streptomycin for
S. Paratyphi B, while NTS has 6 different patterns, which also included the ampicillin-chloramphenicol-spectinomycin-cotrimoxazole- streptomycin pattern. A similar study by Demczuk and colleagues [
35], revealed 26 resistance patterns with the commonest patterns being nalidixic acid-resistant (NAR) and ampicillin-chloramphenicol-nalidixic acid-streptomycin-sulfisoxazole-cotrimoxazole in
S. Typhi compared to this to this study. This study indicated that most of the
Salmonella isolates were resistant to two or more antibiotics and there was variability in the resistant patterns of NTS. The MDR detection rates
S. Typhi,
S. Paratyphi B, and the NTS were all 100%. Similar findings of MDR strains (100%) were reported in Turkey [
36].
All the DEC isolates were highly resistant to cotrimoxazole, ampicillin, cefotaxime, ceftazidime, cefpodoxime, nalidixic acid, and tetracycline. Generally, the isolates showed moderate to high resistance to most drugs, and low resistance to streptomycin and chloramphenicol. Our data suggests the presence of MDR in all the DEC isolates (100%) recovered in this study. This high prevalence of MDR strains observed in this and other studies is worrisome in that it limits treatment options for the patients. Another important observation in this study with the DEC isolates was that they were all resistant to third generation cephalosporins used. Interesting, all the isolates proved to be ESBL-producers. The detection of ESBL-producing DEC isolates warrants attention in the context of increasing resistance amongst the enteropathogens. The high prevalence of ESBL in this study may suggest over prescription of third generation cephalosporins in or inappropriate use of antibiotics in Lusaka.
In this study all the Shigella species were mainly resistant to ampicillin, cotrimoxazole, chloramphenicol and streptomycin, although S. boydii was sensitive to streptomycin. The common resistance pattern was ampicillin-chloramphenicol-cotrimoxazole-streptomycin. These data suggest the presence of MDR in all the Shigella isolates (100%) recovered. This MDR pattern was in consonance with our study.
The two
Campylobacter species isolated in this study were resistant to co-trimoxazole and moderately resistant to both ampicillin and tetracycline. In a Zimbabwean study, 50% of the isolates from humans and 82% from chickens were resistant to co-trimoxazole, while for ampicillin and tetracycline the levels were similar as those in this study. However, MDR resistant isolates were consistently susceptible to erythromycin, chloramphenicol and gentamicin [
37].
Acknowledgments
The authors would also like to thank the nursing, clinical and laboratory staff of the University Teaching Hospital in Lusaka, Zambia, for facilitating the collection of the stool samples, especially Dr. Evans Mpabalwani and Mr. Kelly Mulenga of the Department of Paediatrics and Child Health, and Mr. Joseph Ngulube of the Department of Pathology and Microbiology.