Study in three districts shows 75% of population susceptible to infection

The Health Department has called for intensive surveillance of Severe Acute Respiratory Infections (SARI) and Influenza-like-Illness (ILI) in the community as there is a distinct possibility of another wave of Influenza A (H1N1) infection once rain intensifies.

This year, 34 cases of H1N1 have already been reported from across the State of which 24 cases were reported after the rains began, in May. Since 2009, 3,150 confirmed cases of H1N1 have been reported in the State, including 121 deaths, out of which 32 were ante-natal women.

Influenza cases go up sharply once monsoon begins. In 2009 and 2010, H1N1 cases too went up during monsoon.

Of the 90 H1N1 deaths reported last year, 84 were reported in the rainy season. Cases of H1N1 had dropped dramatically after the monsoon last year but the virus is still in circulation.

“Provisional diagnosis of H1N1 by clinicians has dropped in the past few months because doctors believe that a sizeable section of the community has already been rendered immune to the disease. However, the level of herd immunity is not all that high as we would like to believe,” said Amar Fettle, the State Nodal Officer, H1N1.

In a study conducted last month – an unlinked, anonymous study done for sentinel survey, using leftover blood samples – by Manipal Centre for Virology Research and the State Health Department in the districts of Kannur, Malappuram, and Kozhikode, it was found that the seroprevalence (the frequency of people who have presence of antibodies to H1N1 virus in blood samples) was only about 23-24 per cent.

“This indicates that over 75 per cent of the community is still susceptible to H1N1 infection. This is a new virus and the bigger the size of the un-immune population, the higher the chances of a wave or an outbreak,” Dr. Fettle said. A senior Health official said that given the experience of H1N1 infection among ante-natal population, instructions had been given to all doctors and health field staff to intensify surveillance of ILI among pregnant women. As a precaution, all pregnant women should be started on Oseltamivir as soon as mild influenza symptoms are reported, he said.