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Typhoid fever: a massive, single-point source, multidrug-resistant outbreak in Nepal
Michael D Lewis1, Oralak Serichantalergs, Chittima Pitarangsi
1Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand. Michael.Lewis14@us.army.mil
Summary
A large 2002 typhoid fever outbreak in Nepal was traced to the municipal water supply. Most bacterial isolates were multidrug-resistant, with genetic analysis confirming a single source and resistance mechanisms.
Area of Science:
- Infectious Disease Epidemiology
- Microbiology
- Molecular Epidemiology
Background:
- A significant outbreak of typhoid fever occurred in Bharatpur, Nepal, in 2002, with 5963 cases reported over seven weeks.
- International and local health organizations collaborated to investigate this large, explosive febrile disease outbreak.
Purpose of the Study:
- To conduct a comprehensive epidemiologic and laboratory investigation of the typhoid fever outbreak.
- To determine the size, scope, and molecular origins of the outbreak.
Main Methods:
- Epidemiologic surveillance and case investigation.
- Laboratory analysis of blood samples from febrile patients, including culture and susceptibility testing.
- Molecular techniques such as pulsed field gel electrophoresis (PFGE) and plasmid analysis.
Main Results:
- The majority of bacterial isolates were multidrug-resistant, with resistance linked to plasmids and single-point mutations.
- PFGE analysis demonstrated high similarity (96%-100%) among isolates from patients and the municipal water supply.
- Decreased susceptibility to fluoroquinolones was observed, with 90% of isolates resistant to multiple antibiotics.
Conclusions:
- The outbreak was identified as the largest single-point source outbreak of multidrug-resistant typhoid fever reported to date.
- The outbreak was molecularly linked to the city's municipal water supply.
- Uniform resistance to nalidixic acid and reduced susceptibility to fluoroquinolones characterized the causative agent.