Chennai, April 18 : The Tamil Nadu public health department is taking blood samples and plasma randomly in 888 clusters for the state's second sero survey. The survey will continue till April-end as some districts have commenced the survey after the elections. A total of 26,000 samples will be collected for testing from these 888 clusters. Preliminary results are expected a month after the survey is completed and the main objective of the second sero survey is to find out whether the population has developed herd immunity. The sample population is asked questions related to gender, educational background, age, occupation, travel history which would give a more detailed report on the disease. In Madurai, a total of 1,140 samples from 38 clusters were being collected in the district in the second phase. Coimbatore district has identified 42 clusters and 20 odd blood samples from each cluster was to be collected. In Trichy, there are a total of 32 clusters and 30 houses are there in each cluster. The serum samples will be tested at the Samayanallur Public Health Centre with the help of the CLIA equipment and in Madurai the swabs would be sent to the state public health department laboratory. Director of Public Health Dr. T.S. Selvavinayagam told IANS, "One of the main reasons for the second sero survey is to find out whether the community has developed herd immunity or not." /IANS