Changes in Hemagglutinin and Neuraminidase Genes of pH1N1 Influenza Virus Strains Collected from a North Indian Tertiary Care Hospital during 2015.

OBJECTIVE: The study was conducted to analyze changes in HA and NA genes of pandemic pH1N1 strains, collected from North Indian tertiary care hospital during 2015 and studied the nucleotide change since 2009. Differences in clinical features of cases positive and negative for influenza viruses were also studied.

METHODS: All samples referred for H1N1 testing, were tested for influenza viruses. Randomly selected 25 strains of pH1N1 were studied for nucleotide sequences of HA & NA gene. The nucleotide changes occurring since 2009 were studied by mutational and phylogenetic analysis. Clinical details of cases were recorded and analysed.

RESULTS: A total of 3319 cases of acute respiratory infections (ILI/SARI) were tested for influenza viruses during Jan to April 2015, of which 815 cases tested positive for pH1N1. Nucleotide variation of 2015 strains, from influenza A/California/07/2009 strain at HA1 and NA1 gene was 1.9% and 3.8% respectively. Both HA1 and NA1 coding sequence showed eight mutations. Four of HA1(K180Q, S202T, S220T, and A273T) and NA1 (N200S, V241I, N248D, and N270K) mutations were observed in all pH1N1 study strains.

CONCLUSIONS: Strains of pH1N1 isolated during year 2015 diverged from previously circulating strains. Their association with severity of illness needs to be further studied.