Clinical and Pathological Findings of Fatal 2009–2010 Pandemic Influenza A (H1N1) Infection in Estonia

The aim of this study was to analyze all deaths from A (H1N1) in Estonia during the 2009–2010 epidemic to find out the reasons of high mortality and optimize management strategies for future influenza epidemics.
Material and Methods. A retrospective review of medical records, autopsy reports, and reassessment of autopsy slides of all fatal cases of proven A (H1N1) influenza in Estonia from October 2009 to May 2010 was carried out.
Results. There were a total of 21 proven fatal cases (median age, 57 years); the population mortality rate of 1.56 per 100 000 inhabitants was one of the highest in the world. Altogether, 18 of the 21 patients had known risk factors for influenza, and 3 patients were previously healthy children. Three decedents had received antiviral treatment, and none had been immunized. There were 19 decedents autopsied, with viral pneumonia (58%) being the most frequent pathological finding; 40% had evidence of bacterial superinfection. In 4 cases, influenza was not clinically suspected and was diagnosed postmortem. Influenza was the primary cause of death in 15 decedents, while in 9 cases, comorbidities played a significant role in fatal outcome. In the remaining 4 cases, another illness was considered the primary cause of death with influenza as an accompanying factor.
Conclusions. High autopsy rate and liberal postmortem PCR testing enables the detection of additional A (H1N1) influenza cases, yet it might lead to overestimation of the population mortality rates, especially in a small population with low number of events. Increased vaccine coverage, vigilant diagnosing including wide PCR testing, and early more liberal use of antiviral medications during the influenza A (H1N1) epidemic may hold the potential of lowering population mortality.