A preliminary report by AIIMS has found that the predominately circulating serotypes of dengue virus in Delhi this season are DEN-2 and DEN-4, which are considered "deadly".

"This is based on preliminary data from the first lot of nine acute phase serum samples of suspected cases, which were inoculated into the C6/36 Aedes albowpictus (mosquito) cell line for virus isolation followed by immunoflurescence using dengue type specific anti-bodies for detection and identification.

"Dengue viruses have been isolated from six of these samples and identified as DEN-2 (in four samples) and DEN-4 (in two samples). While DEN-2 was the predominant serotype in circulation during the last two years also, DEN-4 has been isolated very rarely in previous years," said the AIIMS laboratory report.

According to experts, dengue is caused by four serotypes. While types 1 and 3 are mild as they cause dengue fever and fever without shock, type 2 and 4 lead to bleeding and a drop in platelet count and thus are considered deadly.

As per record, 831 people had been diagnosed with dengue in Delhi till August 29 this year. According to the preliminary report, 738 samples have been tested at AIIMS laboratory so far for dengue IgM antibodies and NS1 antigen, of which 314 were found positive.