Clinical Spectrum of Disease. Influenza AH1N1 2009

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In Chile, the first case of 2009 pandemic influenza A H1N1 virus infection was detected on May 17. Since then all influenza like illness cases were notified to Chilean Health Secretary. A total of 367.041 cases were reported, 1585 required hospitalization (0.56%) and 130 died.

The surveillance in Chile shows that the majority of those infected had a mild disease.

The most affected age group was between 5 and 14. Febrile respiratory infection was the most common clinical manifestation and range from self limited to severe illness. In the outpatient group, 97% had fever, 97% headache, 93.5% myalgias, 90% cough, 88.3% sore throat, 84% rhinorrhea, 43.8% join pain, 36% nausea, 29.4% diarrhea. Time between onset symptoms and second case was 3.6 days (range 1 – 9).

Of the 1585 admitted to hospital, 52% were females, median age 33 years (range11 to 94), 56% had underlying medical condition, average time from the onset of illness to hospital admission was 3.6 days. Symptoms at presentation included fever 83%, cough 92.7%, dyspnea 83%, myalgias 63%, hypoxia 50.8%, cyanosis 27.4%, hypotension 18.6%, and 8.3% seizures.

Pneumonia was the diagnosis in 77% patients.

130 patients died, all has been admitted to and ICU. The median age was 44 years (range 4 months to 89 years), 87.5% had underlying medical condition. The cause of death was severe respiratory failure in 34%, septic shock in 19%, bilateral pneumonia 17% and multi organic failure in 16%. Almost all patients received antiviral treatment.

Surveillance in Chile of the 2009 influenza A H1N1 cases allow to characterize the clinical spectrum of the disease in this first pandemic wave.