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C h i l d r e n 's a s t h m a i s m u l t i f a c t o r i a l . Environmental factors like air pollution exposure, meteorological conditions, allergens, and viral infections are strongly implicated. However, place of residence has rarely been investigated in connection with these factors. The primary aim of our study was to measure the impact of particulate matter (PM), assessed close to the children's homes, on asthma-related pediatric emergency hospital visits within the Bouches-du-Rhône area in 2013. In a nested case-control study on 3-to 18-year-old children, each control was randomly matched on the emergency room visit day, regardless of hospital. Each asthmatic child was compared to 15 controls. PM 10 and PM 2.5 , meteorological conditions, pollens, and viral data were linked to ZIP code and analyzed by purpose of emergency visit. A total of 68,897 visits were recorded in children, 1182 concerning asthma. Short-term exposure to PM 10 measured near children's homes was associated with excess risk of asthma emergency visits (adjusted odds ratio 1.02 (95% CI 1.01-1.04; p = 0.02)). Male gender, young age, and temperature were other risk factors. Conversely, wind speed was a protective factor. Conclusion: PM 10 and certain meteorological conditions near children's homes increased the risk of emergency asthma-related hospital visits in 3-to 18-year-old children in Bouches-du-Rhône. What is Known:• A relationship between short-term exposure to air pollution and increase in emergency room visits or hospital admissions as a result of increased pollution levels has already been demonstrated. What is New:• This study confirms these results but took into account confounding factors (viral data, pollens, and meteorological conditions) and is based on estimated pollution levels assessed close to the children's homes, rather than those recorded at the hospital.• The study area, the Mediterranean, is favorable to creation of secondary pollutants in these sunny and dry seasons.

Tropheryma whipplei was detected in preliminary studies in faeces of young children with diarrhoea and also in faeces of asymptomatic persons, not only in Europe but also in Africa. In this study, the link between this bacterium and the presence of acute diarrhoea was evaluated in a large group of children. From December 2009 to January 2013, rectal swabs collected from 3796 children in the emergency departments of university hospitals in Marseille, France, were analysed: 555 children (245 female and 310 male, from 6 days to 6 years old) with acute diarrhoea defined as at least three loose stools per day for <1 week and 3241 children (1444 female and 1797 male, from 22 days to 6 years old) without diarrhoea. Specific quantitative real-time PCR was performed to detect the presence of T. whipplei and of two enteric pathogens Clostridium difficile and Giardia duodenalis. Tropheryma whipplei was significantly more common in children with diarrhoea (22/555, 4%) than without (56/3241, 1.7%; p 0.001). Neither C. difficile nor G. duodenalis showed this association. For C. difficile, 39 of 531 (7.3%) children with diarrhoea were positive versus 184 of 3119 (5.9%) of children without diarrhoea (p 0.25). For G. duodenalis, 2 of 529 (0.37%) children with diarrhoea were positive versus 5 of 3119 (0.16%) children without diarrhoea (p 0.26). Tropheryma whipplei was found more commonly in autumn. Tropheryma whipplei is significantly associated with diarrhoea in children, suggesting that the bacterium may be a cause of acute diarrhoea.