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Arch Med Res. 2012 Oct 15. pii: S0188-4409(12)00246-9. doi: 10.1016/j.arcmed.2012.09.005. [Epub ahead of print]
Epidemiological Characterization of a Fourth Wave of Pandemic A/H1N1 Influenza in Mexico, Winter 2011-2012: Age Shift and Severity.
Borja-Aburto VH, Chowell G, Viboud C, Simonsen L, Miller MA, Grajales-Mu?iz C, Gonz?lez-Bonilla CR, Diaz-Qui?onez JA, Echevarr?a-Zuno S.
Source
Coordinaci?n de Vigilancia Epidemiol?gica y Apoyo en Contingencias, Instituto Mexicano del Seguro Social, Mexico, D.F., Mexico.
Abstract
BACKGROUND AND AIMS:
A substantial recrudescent wave of pandemic influenza A/H1N1 affected the Mexican population from December 1, 2011-March 20, 2012 following a 2-year period of sporadic transmission.
METHODS:
We analyzed demographic and geographic data on all hospitalizations with severe acute respiratory infection (SARI) and laboratory-confirmed A/H1N1 influenza, and inpatient deaths, from a large prospective surveillance system maintained by a Mexican social security medical system during April 1, 2009-March 20, 2012. We also estimated the reproduction number (R) based on the growth rate of the daily case incidence by date of symptoms onset.
RESULTS:
A total of 7569 SARI hospitalizations and 443 in-patient deaths (5.9%) were reported between December 1, 2011, and March 20, 2012 (1115 A/H1N1-positive inpatients and 154 A/H1N1-positive deaths). The proportion of laboratory-confirmed A/H1N1 hospitalizations and deaths was higher among subjects ≥60 years of age (χ(2) test, p <0.0001) and lower among younger age groups (χ(2) test, p <0.04) for the 2011-2012 pandemic wave compared to the earlier waves in 2009. The reproduction number of the winter 2011-2012 wave in central Mexico was estimated at 1.2-1.3, similar to that reported for the fall 2009 wave, but lower than that of spring 2009.
CONCLUSIONS:
We documented a substantial increase in the number of SARI hospitalizations during the period December 2011-March 2012 and an older age distribution of laboratory-confirmed A/H1N1 influenza hospitalizations and deaths relative to 2009 A/H1N1 pandemic patterns. The gradual change in the age distribution of A/H1N1 infections in the post-pandemic period is consistent with a build-up of immunity among younger populations.
Copyright ? 2012 IMSS. Published by Elsevier Inc. All rights reserved.
PMID:
23079035
[PubMed - as supplied by publisher]
Epidemiological Characterization of a Fourth Wave of Pandemic A/H1N1 Influenza in Mexico, Winter 2011-2012: Age Shift and Severity.
Borja-Aburto VH, Chowell G, Viboud C, Simonsen L, Miller MA, Grajales-Mu?iz C, Gonz?lez-Bonilla CR, Diaz-Qui?onez JA, Echevarr?a-Zuno S.
Source
Coordinaci?n de Vigilancia Epidemiol?gica y Apoyo en Contingencias, Instituto Mexicano del Seguro Social, Mexico, D.F., Mexico.
Abstract
BACKGROUND AND AIMS:
A substantial recrudescent wave of pandemic influenza A/H1N1 affected the Mexican population from December 1, 2011-March 20, 2012 following a 2-year period of sporadic transmission.
METHODS:
We analyzed demographic and geographic data on all hospitalizations with severe acute respiratory infection (SARI) and laboratory-confirmed A/H1N1 influenza, and inpatient deaths, from a large prospective surveillance system maintained by a Mexican social security medical system during April 1, 2009-March 20, 2012. We also estimated the reproduction number (R) based on the growth rate of the daily case incidence by date of symptoms onset.
RESULTS:
A total of 7569 SARI hospitalizations and 443 in-patient deaths (5.9%) were reported between December 1, 2011, and March 20, 2012 (1115 A/H1N1-positive inpatients and 154 A/H1N1-positive deaths). The proportion of laboratory-confirmed A/H1N1 hospitalizations and deaths was higher among subjects ≥60 years of age (χ(2) test, p <0.0001) and lower among younger age groups (χ(2) test, p <0.04) for the 2011-2012 pandemic wave compared to the earlier waves in 2009. The reproduction number of the winter 2011-2012 wave in central Mexico was estimated at 1.2-1.3, similar to that reported for the fall 2009 wave, but lower than that of spring 2009.
CONCLUSIONS:
We documented a substantial increase in the number of SARI hospitalizations during the period December 2011-March 2012 and an older age distribution of laboratory-confirmed A/H1N1 influenza hospitalizations and deaths relative to 2009 A/H1N1 pandemic patterns. The gradual change in the age distribution of A/H1N1 infections in the post-pandemic period is consistent with a build-up of immunity among younger populations.
Copyright ? 2012 IMSS. Published by Elsevier Inc. All rights reserved.
PMID:
23079035
[PubMed - as supplied by publisher]
