Seasonality of tuberculosis in Israel, 2001-2011

BACKGROUND: Several studies have suggested that the incidence of tuberculosis (TB) varies with the seasons. OBJECTIVE : To determine the seasonality of TB in Israel and to explore possible associations with climatic variables. METHODS : Laboratory-confirmed TB cases reported between 2001 and 2011 in individuals resident in Israel for at least 1 year before diagnosis were included in the study. Climatic variables included average temperature and average ultraviolet radiation. The mean serum 25- hydroxyVitamin D level of the population was also recorded. RESULT S : Of all 2653 TB cases, incidence peaked during spring (n = 712) and reached its nadir during the fall (n = 577), with a case proportion amplitude (CPA) of 5.1% (P=0.036). Individuals born in the Horn of Africa exhibited a CPA of 9.5% (P = 0.077). Mean population 25-hydroxyVitamin D level was significantly correlated with the seasonal pattern of the disease. Southern Israel had the highest global radiation and, counter-instinctively, the highest TB incidence. CONCLUS IONS : TB exhibited a seasonal tendency in Israel, with the spring peak/fall nadir pattern found elsewhere. Vitamin D is suspected to be an explanatory variable for this seasonal phenomenon. The finding that the highest incidence is in the area receiving the highest global radiation suggests population-related vulnerability to Vitamin D deficiency.