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Nipah Virus Outbreak with Person-to-person Transmission in a District of Bangladesh, 2007

N. HOMA IRA*
Institute of Epidemiology, Disease Control and Research (IEDCR) Dhaka, Bangladesh

M. RAHMAN
Institute of Epidemiology, Disease Control and Research (IEDCR) Dhaka, Bangladesh

M. J. HOSSAIN
International Centre for Diarrhoeal Disease Research, Bangladesh (ICDDR,B), Dhaka, Bangladesh

J. H. EPSTEIN
The Consortium for Conservation Medicine (CCM), New York, USA

R. SULTANA
International Centre for Diarrhoeal Disease Research, Bangladesh (ICDDR,B), Dhaka, Bangladesh

M. S. U. KHAN
International Centre for Diarrhoeal Disease Research, Bangladesh (ICDDR,B), Dhaka, Bangladesh

G. PODDER
International Centre for Diarrhoeal Disease Research, Bangladesh (ICDDR,B), Dhaka, Bangladesh

K. NAHAR
International Centre for Diarrhoeal Disease Research, Bangladesh (ICDDR,B), Dhaka, Bangladesh

B. AHMED
Institute of Epidemiology, Disease Control and Research (IEDCR) Dhaka, Bangladesh

E. S. GURLEY
International Centre for Diarrhoeal Disease Research, Bangladesh (ICDDR,B), Dhaka, Bangladesh

P. DASZAK
Wildlife Trust, New York, NY USA

W. I. L IPK IN
Center for Infection and Immunity, Columbia University, New York, USA

P. E. ROLL IN
Special Pathogens Branch, Division of Viral and Rickettsial Disease, National Centre for Infectious Disease, Centers for Disease Control and Prevention (CDC), Atlanta, GA, USA

J. A. COMER
Special Pathogens Branch, Division of Viral and Rickettsial Disease, National Centre for Infectious Disease, Centers for Disease Control and Prevention (CDC), Atlanta, GA, USA

T. G. KS IAZEK
Special Pathogens Branch, Division of Viral and Rickettsial Disease, National Centre for Infectious Disease, Centers for Disease Control and Prevention (CDC), Atlanta, GA, USA

S. P. LUBY
International Centre for Diarrhoeal Disease Research, Bangladesh (ICDDR,B), Dhaka, Bangladesh

Abstract/ Executive Summary:

In February 2007 an outbreak of Nipah virus (NiV) encephalitis in Thakurgaon District of northwest Bangladesh affected seven people, three of whom died. All subsequent cases developed illness 7–14 days after close physical contact with the index case while he was ill. Cases were more likely than controls to have been in the same room (100% vs. 9. 5%, OR undefined, P<0. 001) and to have touched him (83% vs. 0%, OR undefined, P<0. 001). Although the source of infection for the index case was not identified, 50% of Pteropus bats sampled from near the outbreak area 1 month after the outbreak had antibodies to NiV confirming the presence of the virus in the area. The outbreak was spread by person-to-person transmission. Risk of NiV infection in family caregivers highlights the need for infection control practices to limit transmission of potentially infectious body secretions.

Keywords: Bangladesh, Nipah virus, Person-to-person transmission.

Location: In Bangladesh

Start Date:

End Date:

Program Area: Pest Management

Commodity: Nipah virus

Objectives:

A collaborative team including the Institute of Epidemiology Disease Control and Research (IEDCR) and the International Centre for Diarrhoeal Disease Research, Bangladesh (ICDDR,B), began an investigation on 10 February 2007. The objectives of the investigation were to identify the cause of the outbreak and the risk factors for developing illness.

Methodology:

Case definition and identification We defined suspected case patients as persons having fever with altered mental status or new onset of seizures (severe illness), or persons having fever with headache or cough (mild illness), residing in the outbreak area with an onset of illness between 15 January and 28 February 2007. The team visited the outbreak village and asked the community health workers and community residents if they were aware of any patient who was suffering from fever with seizure or altered mental status, or who had died from these symptoms in their neighborhood. We also asked them about case patients suffering from fever with headache and/ or cough. The team then visited the local hospital in order to identify suspected case patients. Team members also investigated all the deaths in the outbreak village between January and February. We obtained a history of illness and general information about exposures for each suspected case patient. We asked the local health authority of the affected subdistrict to report to the IEDCR if they identified any further suspected case-patient having fever and altered mental status or seizures who sought treatment in the local subdistrict health complex during February.

The team collected blood samples from living suspected case-patients, which were centrifuged in the field and transported on wet ice to IEDCR, where they were stored at x70x. Samples were tested with an immunoglobulin M (IgM) capture enzyme-linked immunosorbent assay (ELISA) that detects IgM antibodies specific for NiV antigens. We defined a confirmed case of NiV infection as a suspected case-patient with detectable IgM to NiV. The team defined a probable NiV case-patient as a patient with fever and altered mental status who lived in the same village as a confirmed case-patient during the outbreak period, but from whom serum was not available because the patient died before a specimen could be collected.

Qualitative study A team of experienced anthropologists conducted in-depth interviews and informal discussions with available confirmed and probable case-patients, their family members and friends, and other residents in these communities with the goals of exploring potential exposures to NiV and identifying appropriate proxy respondents for deceased cases or cases that were too sick to interview. The anthropologists also collected information about symptoms of the disease, caregiving practices and health facility utilization by persons affected by the outbreak.

Case-control study We conducted a case-control study to investigate exposures associated with NiV infection, including person-to-person transmission. Probable and confirmed case-patients were enrolled as cases. We selected three controls for each case-patient. Controls were selected starting from the fourth closest house to the case-patient where no members were ill during the outbreak. The household resident closest in age to the case-patient was eligible to participate as a control. Participation was voluntary. If the selected household resident declined to participate, a resident from the next closest house was asked to participate. The qualitative team selected proxy respondents for each case-patient who had died or was unable to respond. The proxy respondents included family members and friends of the case-patients who were most knowledgeable about their activities and probable risk exposures in the preceding 1 month before illness. Multiple proxy respondents were common. The investigation team used a standardized questionnaire to collect information on demographics, symptoms of illness, and possible risk factors associated with NiV transmission including history of consumption of date palm juice prior to illness, exposure to animals and exposure to ill patients, including touching, staying in the same room, feeding, sharing a bed or cleaning body secretions of a NiV patient.

Bat survey A team of veterinarians from ICDDR,B with assistance from the Consortium for Conservation Medicine located two bat roosts which were 1 km and 15 km distant from the outbreak village. Bats were captured using mist nets and were anesthetized during sample collection and released at the point of capture after sampling from 24 February to 9 March 2007. All the captured bats from which blood samples were collected were P. giganteus. All bat blood samples were kept on ice until the end of each day when serum was separated and stored in liquid nitrogen. At the end of each day, blood samples were transferred to liquid nitrogen and transported to ICDDR,B where they were stored at x70 xC and then shipped on dry ice to the Australian Animal Health Laboratory for laboratory diagnosis. All the blood samples were assayed for antibodies against NiV using a serum neutralization test.

Statistics We analysed socio-demographic and clinical profiles of the case-patients using descriptive statistics. For the case-control study, we used ORs to estimate the association of each exposure with disease and calculated 95% CIs around the ORs. We used the x2 test when expected cell sizes were >5 and Fisher’s exact test when expected cell sizes were <5 and considered the association to be statistically significant if the P value was <0. 05. We used an unmatched analysis because neighbors were chosen as controls to ensure that controls and case-patients were representative of the same population and not to control for confounding factors. Because the primary hypothesis was that the index case was the source of NiV transmission for the subsequent cases, we excluded the index case, but none of the controls in the analyses of person-to person transmission.

Ethics All human study participants gave informed consent for participation in this investigation. The Ethical Review Committee at ICDDR,B reviewed and approved a protocol for encephalitis surveillance and outbreak investigation. Bat capture and sample collection was conducted under a protocol approved by the Institutional Animal Care and Use Committee.

Source of Information: Epidemiol. Infect. (2010), 138, 1630–1636

Article Link (Online Journal): doi:10.1017/S0950268810000695

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Findings from outbreaks in Siliguri and Faridpur illustrate that human-to-human transmission has occurred repeatedly in the Indian subcontinent. The social norm in Bangladesh is that family members and loved ones provide hands-on care to sick patients. Further, hospital healthcare workers in Bangladesh are reluctant to provide hands-on care to admitted patients which increases the risk of transmission to family members and relatives who provide care without any training or supplies to reduce the risk of transmission. Efforts to educate caregivers of their risk especially at later stages of illness, while maintaining sensitivity to cultural mores, and promoting basic infection control practices such as washing hands with soap after handling patients and avoiding close physical contact could limit transmission of NiV and other diseases in people who care for sick patients.

Knowledge Management: Journal