Do environmental factors influence the occurrence of acute meningitis in industrialized countries? An epidemic of varying aetiology in Northern Italy.

Environmental and atmospheric factors have been associated with meningitis epidemics in sub-Saharan Africa but not in the northern hemisphere. An epidemic of meningitis caused by different agents occurred in a health district in northern Italy during the first quarter of 2003: there were 50 cases compared to the expected number of 19, with an incidence rate ratio of 2.7 (95% C.I. = 1.8-3.8). The epidemic occurred concurrently with unusual atmospheric and environmental conditions, such as low temperature, low humidity and elevated PM10. These conditions may have affected local immunity of the pharynx, increasing host vulnerability to acute meningitis. We propose a cumulative index combining temperature, humidity and pollution (THP index), and we set a threshold beyond which an increased risk of acute meningitis may be predicted.