Introduction Changes in meteorological parameters have been associated with stroke occurrence. The incidence of primary intracerebral haemorrhages (PICH) seems to increase in days with cold/mild outdoor temperature. In Portugal, neurologists forward the hypothesis that the incidence of PICH increases in rainy days and not particularly low temperatures. This study aims to study the association between occurrence of PICH and weather parameters.

Methods Data from ACINrpc-project, involving 78 patients suffering a first-ever-in-the-lifetime PICH over a 2-year period in the city of Porto was used. Information on daily weather parameters was obtained from the National Meteorological Office. A Poisson model was used to estimate the association between weather parameters and PICH incidence. Using a conditional logistic regression model, a case-crossover design was then used to estimate the risk of PICH following specific exposures associated with PICH incidence: low diurnal temperature range (DTR) and rainy days. For each subject, the case period was matched with 4 control periods, the same weekday in the previous 4 weeks.

Results PICH incidence increases by 11.8% (95% CI 3.8 to 20.4%) for 1°C drop in DTR and 3.1% (95% CI 1.1 to 5.1%) for a 1 mm/m² in precipitation. Following a day with a DTR<4°C the OR is 2.9 (95% CI 1.4 to 5.8), increasing to 8.8 (95% CI 1.7 to 44.8) after a 48 h exposure. Following days with low DTR and rain, the OR is 3.2 (95% CI 1.3 to 8.1) and 9.5 (95% CI 1.1 to 88.9) for a precipitation>10 mm/m² and 40 mm/m², respectively.

Conclusion Precipitation by itself is not associated with PICH incidence, nevertheless has a synergistic effect in low DTR days.