Rapid estimation of excess mortality during the COVID-19 pandemic in Portugal: beyond reported deaths

BACKGROUND: One month after the first COVID-19 infection was recorded, Portugal counted 18,051 cases and 599 deaths from COVID-19. To understand the overall impact on mortality of the pandemic of COVID-19, we estimated the excess mortality registered in Portugal during the first month of the epidemic, from March 16 until April 14 using two different methods.

METHODS: We compared the observed and expected daily deaths (historical average number from daily death registrations in the past 10 years) and used 2 standard deviations confidence limit for all-cause mortality by age and specific mortality cause, considering the last 6 years. An adapted Auto Regressive Integrated Moving Average (ARIMA) model was also tested to validate the estimated number of all-cause deaths during the study period.

RESULTS: Between March 16 and April 14, there was an excess of 1255 all-cause deaths, 14% more than expected. The number of daily deaths often surpassed the 2 standard deviations confidence limit. The excess mortality occurred mostly in people aged 75+. Forty-nine percent (49%) of the estimated excess deaths were registered as due to COVID-19, the other 51% registered as other natural causes.

CONCLUSION: Even though Portugal took early containment measures against COVID-19, and the population complied massively with those measures, there was significant excess mortality during the first month of the pandemic, mostly among people aged 75+. Only half of the excess mortality was registered as directly due do COVID-19.

KEY POINTS:

An Excess Mortality (EM) of 1255 deaths were estimated 1 month after the first death classified by COVID-19, and it would probably be more if the government had not taken early action.

The age group where a significant increase in mortality was noted was above 75 years.

51% of the EM was due to natural causes other than COVID-19.