Regional solar radiation is inversely correlated with incidence and severity of tuberculosis in Chile

Vitamin D (VD) deficiency has been linked to increased incidence and morbidity of tuberculosis (TB). Chile has large variations in solar radiation (SR; a proxy of VD status) and high prevalence of VD deficiency in its southernmost regions with low SR. We investigated the correlation between regional SR and rates of TB incidence, admissions and deaths in Chile by reviewing national records on prospectively collected mandatory disease notifications, admissions and mortality between 2001 and 2011. Over the study period, 26 691 new TB notifications were registered. The TB incidence rate was 14·77 (95% confidence intervals (CIs) 14·60-14·95), admission rate was 12·12 (95% CI 11·96-12·28) and mortality rate was 1·61 (95% CI 1·55-1·67) per 100 000 population per year. Multivariable linear regressions adjusting for significant demographic TB risk factors in Chile (regional prevalence of HIV infection, rates of migration from TB-endemic countries and rates of imprisonment) revealed an independent and highly statistically significant inverse association between SR and TB incidence rate (β -1·05, 95% CI -1·73 to -0·36, P = 0·007), admission rate (β -1·58, 95% CI -2·23 to -0·93, P < 0·001), and mortality rate (β -0·15, 95% CI -0·23 to -0·07, P = 0·002). These findings support a potential pathogenic role of VD deficiency in TB incidence and severity.