Outbreak investigation and assessment of determinants of ceftriaxone resistant salmonella typhi outbreak from Hyderabad, Pakistan : a matched case-control study

Date of Award


Document Type


Degree Name

Master of Science in Epidemiology & Biostatistics (MSc Epidemiology & Biostats)


Community Health Sciences


Typhoid fever, caused by Salmonella serovar typhi (S. typhi), is one of the commonest febrile illnesses encountered in developing countries. Approximately 21 million cases and 222,000 typhoid-related deaths occur annually worldwide. Multiple outbreaks due to multidrug resistant (MDR) S. typhi have been reported from various parts of the world. On 29th November 2016, first case of ceftriaxone resistant S. typhi was reported by The Aga Khan University Hospital clinical laboratory from Hyderabad. We conducted an outbreak investigation aiming at describing the magnitude of outbreak, generating a 'spot map' for clustering of cases and identifying determinants of ceftriaxone resistant S. typhi outbreak. Methodology: We carried out an age and area matched 1:4 case control study from 1 st December 2016 to July 15, 2017.We defined the case as a resident of Hyderabad who had positive blood culture for ceftriaxone resistant S. typhi from 28th November onwards. Controls were residents living in the same catchment area as of cases, who had been otherwise healthy within four weeks before the interview. We defined suspected case as one with > 3 days of fever without focus. We administered a questionnaire to study participants to identify various exposures, collected water samples for microbiological analysis and venous blood samples were drawn from suspected cases. Conditional logistic regression was performed and matched odds ratio (MOR) with 95 % confidence intervals is reported. Results: A total of 325 blood culture confirmed cases of ceftriaxone resistant S. typhi were identified till 20th July 2017. Males constituted 59 % of the cases and majority (88%)were children < 10 years of age. A total of 142 cases and 568 matched controls were enrolled. Median age of cases was 4 years (IQR 4.06). In a conditional logistic regression model, drinking un-safe water (84.5 % vs. 72.7 %, MOR 2.06, 95 % CI 1.26 — 3.38), using antibiotics 2 weeks before being sick (32.39 % vs. 10.39 %, MOR 4.46, 95 % CI 2.78 — 7.17), history of travel four weeks before being ill (39.44 % vs. 20.95 %, MOR 2.47, 95 % CI 1.66 — 3.68) and contact with typhoid patient in last 4 weeks (20.42 % vs. 5.98 %, MOR 4.30, 95 % CI 2.44 — 7.57) were independently associated with ceftriaxone resistant S. typhi fever. One typhoid related death has been reported in this outbreak (case fatality rate 0.31 %). Conclusion: Drinking unsafe water, contact with typhoid patient and previous use of antibiotics was identified as independent risk factors for this outbreak. Vaccination of at risk population and safe potable water supply are the most important measures for the control of this outbreak.

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