Impact of the novel influenza A (H1N1) during the 2009 autumn-winter season in a large hospital setting in Santiago, Chile.
BACKGROUND
In Chile, the novel influenza A (H1N1) epidemic began in the middle-high income area of Santiago. Clinical and laboratory surveillance was intensified with the aim to characterize the epidemic and determine its impact in a large hospital setting.


METHODS
Demographic and clinical data were obtained from all patients whose symptoms met the clinical definition of influenza A (H1N1) infection during the epidemic period. Laboratory confirmation was obtained by use of a nasopharyngeal antigen detection test for influenza A and/or influenza A (H1N1) polymerase chain reaction (PCR). A case was considered confirmed if the antigen detection test result for influenza A and/or the PCR test result were positive.


RESULTS
The total number of emergency department (ED) visits increased by 88.5% from a mean of 14,489 ED visits in 2006-2008 to a mean of 27,308 ED visits in 2009, during the epidemic period. There were 10,048 patients who were clinically diagnosed with influenza A (H1N1), and they represented 78% of all visits, of which 4591 (45.6%) were laboratory confirmed. The median time from symptom onset to diagnosis was 1 day, and 99.7% of individuals received antiviral treatment. School-aged children represented 67% of ED visits at the beginning of the epidemic and 24% of ED visits at the end of the epidemic. Only 2% of cases were hospitalized; of these, 70% of cases occurred in patients 6-50 years of age, and 32% of cases occurred in patients who had an underlying medical condition. Eleven patients (age range, 1-53 years) required admission to the intensive care unit (ICU); 6 of these patients had pneumonia with or without hemodynamic shock. No influenza-associated deaths occurred.


CONCLUSIONS
Many cases of influenza A (H1N1) occurred in school-aged and adult individuals who required an ED visit; these visits resulted in a low impact on the use of hospital beds. Aggressive ICU management and/or experience in extracorporeal membrane oxygenation significantly improved outcomes. Early antiviral treatment may have played an important role in the low number of severe cases. Vaccines targeted for school-aged children and young adults may modify the first epidemic wave in the northern hemisphere.
Torres
Juan Pablo
JP
Department of Pediatrics, Division of Pediatric Infectious Diseases, Faculty of Medicine, Universidad de Chile, Santiago, Chile. jptorres@clc.cl
O'Ryan
Miguel
M
Herve
Beatrice
B
Espinoza
Ricardo
R
Acuña
Guillermo
G
Mañalich
Jaime
J
Chomalí
May
M
D000293:Adolescent; D000328:Adult; D000956:Antigens, Viral / Q000032:analysis; D000998:Antiviral Agents / Q000627:therapeutic use; D002648:Child; D002675:Child, Preschool; D002677:Chile / Q000453:epidemiology; D004636:Emergency Service, Hospital; D005260:Female; D006761:Hospitals; D006801:Humans; D007223:Infant; D053118:Influenza A Virus, H1N1 Subtype / Q000302:isolation & purification*; D007251:Influenza, Human / Q000453:epidemiology* / Q000473:pathology / Q000628:therapy / Q000821:virology*; D008297:Male; D008875:Middle Aged; D009305:Nasopharynx / Q000821:virology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D055815:Young Adult
D000956:Antigens, Viral; D000998:Antiviral Agents