BACKGROUND: Pneumonia is one of the complications of COVID-19 . Primary care electronic health records (EHR) have shown the utility as a surveillance system . We therefore analyse the trends of pneumonia during two waves of COVID-19 pandemic in order to use it as a clinical surveillance system and an early indicator of severity .

METHODS: Time series analysis of pneumonia cases, from January 2014 to December 2020 . We collected pneumonia diagnoses from primary care EHR, a software system covering> 6 million people in Catalonia (Spain). We compared the trend of pneumonia in the season 2019-2020 with that in the previous years . We estimated the expected pneumonia cases with data from 2014 to 2018 using a time series regression adjusted by seasonality and influenza epidemics .

RESULTS: Between 4 March and 5 May 2020 , 11,704 excess pneumonia cases (95% CI : 9909 to 13,498) were identified . Previously, we identified an excess from January to March 2020 in the population older than 15 years of 20% . We observed another excess pneumonia period from 22 october to 15 november of 1377 excess cases (95% CI : 665 to 2089). In contrast, we observed two great periods with reductions of pneumonia cases in children, accounting for 131 days and 3534 less pneumonia cases (95% CI , 1005 to 6064) from March to July; and 54 days and 1960 less pneumonia cases (95% CI 917 to 3002) from October to December .

CONCLUSIONS: Diagnoses of pneumonia from the EHR could be used as an early and low cost surveillance system to monitor the spread of COVID-19.