Study design and study area
A descriptive cross-sectional study was carried out between 2017 and 2018 to describe the epidemiology of the cholera epidemic of in Kasese district, Uganda (Fig. 1). Kasese district lies along the equator and it is bordered by the districts of Kabarole to the north, Rubirizi to the south, Kamwenge to the east and the Democratic Republic of Congo to the West. The biggest population of the district live in rural areas and practicing subsistence farming. With a population of 757,269 people and 134,037 being children below 5 years the leading cause of morbidity was malaria and acute diarrhea; which is also a major presenting symptom for cholera was the second leading cause of morbidity. Cholera ranked as the third most important cause of Morbidity (10).
Study population and sampling
The study population comprised of both adults and children suspected to be suffering from cholera admitted in the isolation wards in Kagando hospital and Bwera hospital. According to the World Health Organization’s standard case definition: if cholera is not known to be present in the area, a case is a patient ≥ 5 years with severe dehydration or death from acute watery diarrhea, while during the epidemic, every patient ≥5 years with acute watery diarrhea and/or vomiting is considered a case (11). In the community, the patients who were discharged from the isolation wards or their parents/guardians formed the study population. Consecutive sampling was carried out throughout the outbreak season until the time when the epidemic was controlled. Sample size calculation was not applicable.
A list of discharged patients was obtained from the isolation units of Bwera hospital and Kagando hospital and the individuals were followed to the community where they live. A total of 222 patients were recorded in the discharge book some of whom were children and these were followed to the community. We obtained telephone contacts of the care takers and worked with community health workers to locate the cases. Key questions on symptomatology and environment were asked. Major symptoms looked out for included acute diarrhea, vomiting and abdominal cramps. Environmental assessment was carried out using an environmental checklist. The key elements of the environmental checklist included; safe water, food safety, sanitation and hygiene, personal, family and school hygiene, municipal water supplies, other water supplies, solid waste disposal, disposal of excreta and treatment of waste water. We also took GPS points of the homes of the cases and pictures of potential source infection (Fig. 1).
Laboratory detection of Vibrio cholerae
Self-collected rectal swabs from suspected case-persons were transported to the laboratory in alkaline peptone water medium for culture and sensitivity. ‘Case-persons’ is used in this study to mean persons with signs and symptoms matching the standard definition for the cholera case (11). The samples were cultured on Thiosulphate-Citrate-Bile-Salts Sucrose (TCBS™; SEIKEN Japan) agar and incubated at 370C for 18-24 hours. The isolates were serotyped with polyvalent 01 antiserum and monovalent serotype Inaba and Ogawa antisera (Denka Seiken, Tokyo, Japan). Rectal swabs were collected from 71 participants and antibiotic susceptibility done in Bwera hospital and Kagando Hospital laboratories.
Antibiotic susceptibility testing
Antimicrobial susceptibility testing was performed using the Kirby-Bauer disk diffusion method on Mueller-Hinton agar. The Escherichia coli reference strain ATCC 25922 was used as a control. Isolates were tested against 7 antimicrobial drugs as follows: ampicillin (10μg), ciprofloxacin (5 μg), chloramphenicol (30μg), gentamycin (30μg), nalidixic acid (30μg), Sulfamethoxazole/trimethoprim (1.25 μg + 23.75 μg) and tetracycline (30μg) (all Oxoid, United Kingdom). Zones of inhibition were interpreted according to the 2014 Clinical and Laboratory Standards Institute (CLSI) guidelines as resistant and susceptible (12).
Potential sources of bias
Recall bias was the most common potential confounder as recollection of previous events might have been difficult for our respondents. However, the authors tried to minimize this by administering the questionnaires during the outbreak season to benefit from fresh memories.
Ethical approval was obtained from the Makerere University School of Biomedical Sciences Higher Degrees Research and Ethics committee (SBS-292). Written informed consent was obtained from all study participants. Consent from parents/guardians of participants below 18 years was sought and ascent was obtained from all minors who took part in this study. Participation was voluntary.
Data management and presentation
Data was checked for completeness to avoid cases of missing data and entered in Microsoft Excel. The variables of interest collected include; age sex, date of onset of symptoms, date of admission, duration of hospitalization, outcome and laboratory results, recovery and death. Cleaned data was exported to STATA v14 for analysis in time, place and person and presented in form of Tables and Figures.