Role of climate in the spread of shiga toxin-producing Escherichia coli infection among children

Hemolytic-uremic syndrome (HUS) is a rare disease mainly affecting children that develops as a complication of Shiga toxin-producing Escherichia coli (STEC) infection. It is characterised by acute kidney injury, platelet consumption, and the mechanical destruction of red blood cells (hemolysis).In order to test the working hypothesis that the spread of the infection is influenced by specific climatic conditions, we analysed all of the identified cases of infection occurring between June 2010 and December 2013 in four provinces of Lombardy, Italy (Milano, Monza Brianza, Varese and Brescia), in which a STEC surveillance system has been developed as part of a preventive programme. In the selected provinces were recorded in few days a great number of cases, clusters which are unrelated for spatially distant or for the disease is caused by different STEC serotypes. In order to investigate a common factor that favored the onset of infection we have analysed in detail the weather conditions in the areas. The daily series of temperature, rain and relative humidity were studied to show the common climate peculiarities while the correlation coefficient and the Principal Component Analysis, PCA, were used to point out the meteorological variable, maximum temperature, as the principal climate element in the onset of the infection. The use of Distributed Lag Non-Linear Models, DLNM, and the climate indices characterising Heat Waves, HW, has allowed to identify the weather conditions associated with STEC infection. The study highlighted a close temporal correlation between STEC infection in children and the number, duration and frequency of heat waves. In particular if maximum temperature is greater than 90th percentile, days classificated as very hot, for 3 or more consecutive days the risk of infection increasing.