Infection and death from influenza A H1N1 virus in Mexico: a retrospective analysis.
BACKGROUND
In April, 2009, the first cases of influenza A H1N1 were registered in Mexico and associated with an unexpected number of deaths. We report the timing and spread of H1N1 in cases, and explore protective and risk factors for infection, severe disease, and death.


METHODS
We analysed information gathered by the influenza surveillance system from April 28 to July 31, 2009, for patients with influenza-like illness who attended clinics that were part of the Mexican Institute for Social Security network. We calculated odds ratios (ORs) to compare risks of testing positive for H1N1 in those with influenza-like illness at clinic visits, the risk of admission for laboratory-confirmed cases of H1N1, and of death for inpatients according to demographic characteristics, clinical symptoms, seasonal influenza vaccine status, and elapsed time from symptom onset to admission.


RESULTS
By July 31, 63 479 cases of influenza-like illness were reported; 6945 (11%) cases of H1N1 were confirmed, 6407 (92%) were outpatients, 475 (7%) were admitted and survived, and 63 (<1%) died. Those aged 10-39 years were most affected (3922 [56%]). Mortality rates showed a J-shaped curve, with greatest risk in those aged 70 years and older (10.3%). Risk of infection was lowered in those who had been vaccinated for seasonal influenza (OR 0.65 [95% CI 0.55-0.77]). Delayed admission (1.19 [1.11-1.28] per day) and presence of chronic diseases (6.1 [2.37-15.99]) were associated with increased risk of dying.


CONCLUSIONS
Risk communication and hospital preparedness are key factors to reduce mortality from H1N1 infection. Protective effects of seasonal influenza vaccination for the virus need to be investigated.


BACKGROUND
None.
Echevarría-Zuno
Santiago
S
Dirección de Prestaciones Médicas, Instituto Mexicano del Seguro Social, Mexico City, Mexico.
Mejía-Aranguré
Juan Manuel
JM
Coordinación de Vigilancia Epidemiológica y Apoyo en Contingencias, Unidad de Salud Pública, Dirección de Prestaciones Médicas, Instituto Mexicano del Seguro Social, Mexico City, Mexico.
Mar-Obeso
Alvaro J
AJ
Coordinación de Vigilancia Epidemiológica y Apoyo en Contingencias, Unidad de Salud Pública, Dirección de Prestaciones Médicas, Instituto Mexicano del Seguro Social, Mexico City, Mexico.
Grajales-Muñiz
Concepción
C
Coordinación de Vigilancia Epidemiológica y Apoyo en Contingencias, Unidad de Salud Pública, Dirección de Prestaciones Médicas, Instituto Mexicano del Seguro Social, Mexico City, Mexico.
Robles-Pérez
Eduardo
E
Coordinación de Vigilancia Epidemiológica y Apoyo en Contingencias, Unidad de Salud Pública, Dirección de Prestaciones Médicas, Instituto Mexicano del Seguro Social, Mexico City, Mexico.
González-León
Margot
M
Coordinación de Vigilancia Epidemiológica y Apoyo en Contingencias, Unidad de Salud Pública, Dirección de Prestaciones Médicas, Instituto Mexicano del Seguro Social, Mexico City, Mexico.
Ortega-Alvarez
Manuel Carlos
MC
Coordinación de Vigilancia Epidemiológica y Apoyo en Contingencias, Unidad de Salud Pública, Dirección de Prestaciones Médicas, Instituto Mexicano del Seguro Social, Mexico City, Mexico.
Gonzalez-Bonilla
Cesar
C
Coordinación de Vigilancia Epidemiológica y Apoyo en Contingencias, Unidad de Salud Pública, Dirección de Prestaciones Médicas, Instituto Mexicano del Seguro Social, Mexico City, Mexico.
Rascón-Pacheco
Ramón Alberto
RA
Coordinación de Vigilancia Epidemiológica y Apoyo en Contingencias, Unidad de Salud Pública, Dirección de Prestaciones Médicas, Instituto Mexicano del Seguro Social, Mexico City, Mexico.
Borja-Aburto
Víctor Hugo
VH
Coordinación de Vigilancia Epidemiológica y Apoyo en Contingencias, Unidad de Salud Pública, Dirección de Prestaciones Médicas, Instituto Mexicano del Seguro Social, Mexico City, Mexico. Electronic address: victor.borja@imss.gob.mx.
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D002908:Chronic Disease; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D053118:Influenza A Virus, H1N1 Subtype; D007252:Influenza Vaccines; D007251:Influenza, Human / Q000453:epidemiology* / Q000401:mortality / Q000517:prevention & control; D008297:Male; D008800:Mexico / Q000453:epidemiology; D008875:Middle Aged; D012189:Retrospective Studies
D007252:Influenza Vaccines