Title: Investigations of Recurrent outbreaks of unknown fever, establish rural dengue activity in West Midnapore, a costal district in West Bengal, India.Background: In the year 2002, an investigation was conducted for the diagnosis of an unknown fever outbreak in the District of West Midnapore, West Bengal; on request of the Director of Medical Education, Govt. of West Bengal. In the year 2004, again unknown fever outbreak took place in some other area of same district and that too was investigated on request of the State Medical Department. The recurrence of same episodein the year 2007 was investigated by the local medical team and the collected serum samples were sent to us for laboratory based conformation.
Methods and findings: During the first episode (2002), a total of 1158 fever cases were reported with 7 deaths, which spread all over the district since 2nd week of May till 15th July, 2002. In the second episode (2004), 792 cases were reported and 2 deaths were recorded. A total of 781 acute sera samples could be collected during these three consecutive out breaks. The samples were collected from the patients with clinical featuresof fever with head ache, body ache, nausea, retro orbital pain, abdominal pain and rashes of duration 2-7 days, which is closely related with the symptoms of dengue infection. Only 195 convalescent sera were made available. Acute samples were tested for the presence of dengue specific IgM antibodies by ELISA method. There was a significantly higher incidence of fever cases in children belonging to the age group up to 10 years.No virus could be isolated from the acute sera collected from fever cases. The results of serological survey showed the presence of IgM antibodies to Dengue virus in only in 446 (57%) of the acute cases. Amongst the195 convalescent sera, four fold rise of HAI Antibody titre to Dengue viruswas observed only in 77 (39%).
Conclusion: Analysis of the epidemiological and serological findings of different years revealed that the out breaks were due to Dengue infection. Children up to 10 years of age in this district were mostly affected during these out breaks.