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Chikungunya epidemic in India may have been underreported
Inaccuracies in reporting possibly underplayed the mortality rates associated with the chikungunya epidemic.
In 2006, nearly 3,000 people died in a four-month period in an Indian city during an outbreak of chikungunya virus. However, no deaths were attributed to the disease by the government of India.
Researchers from the Indian Institute of Management in Ahmedabad, India, compared morality rates in the city from August 2006 through November 2006 with deaths during the same months in the four years prior to the epidemic. The goal was to assess mortality associated with the epidemic and see if the virus has increased virulence.
The city has an estimated population of 3.8 million. Chikungunya is native to tropical Africa and Asia, but reports of suspect cases have been reported in Italy and France. A chikungunya epidemic on Reunion Island in the Indian Ocean in 2005-2006 was attributed to 254 deaths by French public health authorities.
Because of high mortality rates found during the epidemic in India, the researchers indicated that hidden mortality may have occurred during the chikungunya epidemic in other parts of India also.
Public health officials should investigate suspected chikungunya virus epidemics and implement measures to prevent future epidemics, especially in developing countries where underreporting or misreporting of epidemics and deaths may occur, according to the researchers.
The researchers also called for revision of the epidemic numbers because of possible faulty reporting. Ten people died from chikungunya virus, according to the city health authorities, but the Indian government reported no deaths attributable to chikungunya. Inaccuracies in epidemic reporting in developing countries further hamper international travel warning systems, the researchers wrote.
The study results were published in Emerging Infectious Diseases.
Chikungunya in India
The attack rate for chikungunya was 37.5% in India during a 1973 epidemic. The attack rate in 2006 reached 45% in some areas. During the 2006 epidemic, more than 1.39 million cases were reported across 151 districts in 10 states.
Although no deaths were directly attributed to chikungunya by the government, researchers have linked about 3,000 additional deaths to the epidemic in Ahemdabad.
The average mortality rate was calculated for each month in the years prior to the epidemic and for each month within the epidemic year (2006). The average monthly mortality rates for each month and year were compared with the mortality rates of the epidemic year.
Death reports used in this study were from 2002 to 2006, and all were provided by the state registrars. Deaths in Ahmedabad are reported two ways: if a death occurs in a hospital, a medical certificate is issued by hospital staff and is then forwarded to a city registrar. Deaths at home are reported to the local registrar by relatives.
During the 2006 epidemic, the city health department collected data on suspected chikungunya cases reported from public hospitals and health centers only. Few data were provided from private hospitals, dispensaries and private doctors.
The researchers cited poor reporting of cases and deaths as a hindrance to accuracy of numbers affected by the epidemic.
In 2006, there were 60,777 suspected cases of chikungunya in Ahmedabad reported. In August and September of that year, 55,593 (91.5%) of cases were reported. More than half of the 154 blood samples taken tested positive for chikungunya virus. Eighty-four chikungunya cases were confirmed, and 10 were fatal. Fatalities included two people aged older than 80 years, four people aged 60 to 70 years and three people aged younger than 60 years. The mortality rate was 11.9%.
Mortality rates high
Mortality rates per month in 2006 increased 22% in August, 57% in September and 33% in October compared with average monthly mortality rates in the four previous years.
About 3,056 more deaths were registered in Ahmedabad in 2006 when compared with expected deaths based on previous years. In the period from August through November, 2,944 additional deaths which accounted for 96.34% of total additional deaths in 2006, occurred in the city when compared with the same period in the prior four years. – Kirsten H. Ellis
For more information:
- Mavalankar D, Shastri P, Bandyopadhyay T, et al. Increased mortality rate associated with chikungunya epidemic, Ahmedabad, India. Emerg Infect Dis. 2008;www.cdc.gov/eid/content/14/3/pdfs/07-0720.pdf.