Distance from sea as determinant of geographic variation of tuberculosis in India.
A cluster sample survey of the point-prevalence of microbiologically confirmed pulmonary tuberculosis (MCPTB) in the population above 14 years of age in India, by the Indian Council of Medical Research, revealed unexpectedly wide geographic variations across states, with a distinct and intriguing pattern: coastal states consistently had lower prevalence rates than land-locked states. The odds of having a prevalence rate above the mean are 46 times higher for land-locked compared to coastal states. The lowest rate was in Kerala, a state with a long seacoast, and the highest in Delhi National Capital Region, landlocked and far from any seacoast. We hypothesize that constant air exchange with sea air without any Mycobacterium tuberculosis, has led to lower risk of infection, eventually expressed as lower prevalence of MCPTB. Understanding this determinant of geographic variation provides valuable insights for strategies aimed at controlling tuberculosis.