- Design
- Systematic review of epidemiological parameters and models
- Population
- 119 papers covering 23 Nipah virus outbreaks
- Primary outcome
- Incubation, case fatality and transmission parameters
- Effect
- Median incubation 8.8 days (7.5–10.0); case fatality 9% to 82%
A systematic review published in July drew 243 epidemiological parameters, 23 outbreaks and 39 mathematical models from 119 papers on Nipah virus.
The pooled median incubation period was about 8.8 days (95% CI 7.5–10.0), from eight estimates. Case-fatality ratios ranged from 9% in Singapore to 82% in Bangladesh. Four of five estimates of the basic reproduction number were below one, meaning most outbreaks burn out, but transmission data were thin and few models had been fitted to data.
For clinicians in Kerala and West Bengal, where outbreaks recur, the incubation estimate is the most practical number: it supports contact follow-up for at least two to three weeks. The wide fatality range likely reflects differences in strain, exposure route and access to intensive care.
- Consider Nipah in acute encephalitis or severe respiratory illness during an outbreak or after bat or date palm sap exposure.
- Isolate suspected cases early and use full respiratory and contact precautions.
- Follow contacts for at least three weeks, given an incubation that can exceed two weeks.
- Notify the district surveillance unit immediately on suspicion.
Why it matters
Contact tracing decisions in an outbreak depend on an incubation period that has been poorly defined.
Don't overread it
The parameters come from a small number of outbreaks, and the review pooled heterogeneous reports.
The statistics, in plain English
A reproduction number below one means each case infects fewer than one other on average, so chains tend to end. Estimates were few, so this is not a guarantee in any single outbreak.
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