Secondary Attack Rate for Nipah Virus Infection
The secondary attack rate for Nipah virus among close contacts ranges from approximately 50% in household settings, with person-to-person transmission documented in roughly half of all recognized cases in Bangladesh outbreaks. 1
Documented Transmission Patterns
Person-to-Person Transmission Frequency
- Approximately 50% of recognized Nipah virus cases in Bangladesh developed their disease following person-to-person transmission, making human-to-human spread a major contributor to outbreak propagation 1
- In the 2001 Meherpur outbreak, 7 of 13 cases (54%) occurred in persons from just two households, demonstrating intense household clustering 2
- In the 2003 Naogaon outbreak, 7 of 12 cases (58%) were clustered in 2 households, again showing high secondary attack rates in close contact settings 2
Risk Factors for Secondary Transmission
- Patients were significantly more likely to develop disease if they had close contact with other patients, establishing direct person-to-person contact as a primary risk factor 2
- Exposure to infected patients' saliva represents a critical transmission route that family members and caregivers must avoid 1
- Human transmission occurs through close contact with infected individuals, particularly in healthcare and household settings 3
Clinical Context and Outbreak Characteristics
Disease Severity and Mortality
- The case fatality rate ranges from 40% to 75%, making prevention of secondary transmission critically important for outbreak control 4, 3
- Clinical manifestations range from mild respiratory illness to severe and fatal encephalitis, with the severity influenced by healthcare availability, patient condition, and viral strain virulence 3
Geographic Distribution
- Eight outbreaks have been reported from Bangladesh since 2001, with recurring patterns of household clustering 1
- The virus has been documented in Malaysia, Bangladesh, and India, with fruit bats (genus Pteropus) serving as natural reservoirs 3
Prevention Strategies
Primary Prevention Measures
- Decreasing bat access to date palm sap prevents primary transmission from the reservoir host 1
- Reducing family members' and friends' exposure to infected patients' saliva is essential for preventing secondary cases 1
Surveillance Recommendations
- Enhanced surveillance and diagnostic capacity to detect Nipah virus infection are recommended following any suspected outbreak 2
- Early detection and prompt response are crucial for controlling outbreaks, though diagnostic challenges and delayed recognition remain significant barriers 3
Healthcare Worker Protection
- Hospital workers in the investigated outbreaks tested negative for Nipah virus antibodies, suggesting that appropriate infection control measures can prevent nosocomial transmission 2
Important Caveats
The high secondary attack rate in household settings (approximately 50%) contrasts sharply with other infectious diseases and demands aggressive isolation and contact precaution measures. Unlike the meningococcal disease secondary attack rate of 4 per 1,000 household contacts 5, Nipah virus demonstrates far more efficient person-to-person transmission in close contact settings. The clustering of cases within households and the documented transmission through saliva exposure underscore the need for strict respiratory and contact precautions when managing suspected or confirmed cases.