Trends in non-polio acute flaccid paralysis incidence in India 2000-2013

BACKGROUND: Although the incidence of polio acute flaccid paralysis (AFP) has decreased in India, the nonpolio AFP (NPAFP) rate has increased. Nationwide, the NPAFP rate is 11.82 per 100 000 population, whereas the expected rate is 1 to 2 per 100000 population. We examined the correlates of NPAFP to discern explanations for the increase. The incidence of polio AFP in India has decreased. However, the nonpolio AFP rate has increased since 2000. Follow-up of these cases of nonpolio AFP is not done routinely. However, one-fifth of these cases of nonpolio AFP in the state of Uttar Pradesh (UP) were followed up after 60 days in 2005; 35.2% of patients were found to have residual paralysis, and 8.5% had died. This suggests that the pathology in children being registered as having nonpolio AFP cannot be considered trivial. Therefore, there is a compelling reason to try to determine the underlying causes for the surge in nonpolio paralysis numbers. METHODS: The data on AFP, polio and nonpolio AFP, and the number of polio rounds were examined in each state in each year from 2000 to 2013. Multiple linear regression analysis adjusting for region or state, total and female literacy rate, population density, and the per-capita gross domestic product was performed. Differences between states and changes over time were analyzed. RESULTS: NPAFP increased with the number of oral polio vaccine (OPV) doses used (R2 5 25.02%; P, .001). When the effect of cumulative doses over the previous years was examined, the NPAFP rate in 2013 best correlated with the cumulative doses received in the previous 7 years (R2 5 57.16%), with 2012 excluded because data for this year were incomplete. This correlation was highly significant (P, .001). On multiple regression analysis, the number of OPV doses was the only factor that showed a positive correlation with the NPAFP rate. The average increase in the NPAFP rate was 1.31 per 100 000 population (P, .001; 95% confidence interval, 1.11–1.52) with each dose of OPV. The NPAFP rate in UP and Bihar, which had consistently increased each year until 2011, decreased in the 2 states in 2012, coinciding with a reduction in doses of OPV administered. CONCLUSIONS: The incidence of NPAFP was strongly associated with the number of OPV doses delivered to the area. A dose-response relationship with cumulative doses over the years was also observed, which strengthens the hypothetical relationship between polio vaccine and NPAFP. The fall in the NPAFP rate in Bihar and UP for the first time in 2012, with a decrease in the number of OPV doses delivered, is evidence of a causative association between OPV doses and the NPAFP rate.