Epidemiological Characterization of a Fourth Wave of Pandemic A/H1N1 Influenza in Mexico, Winter 2011-2012

Age Shift and Severity

Víctor H. Borja-Aburto, Gerardo Chowell, Cécile Viboud, Lone Simonsen, Mark A. Miller, Concepción Grajales-Muñiz, Cesar R. González-Bonilla, Jose A. Diaz-Quiñonez, Santiago Echevarría-Zuno

Research output: Contribution to journalArticle

27 Citations (Scopus)

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 (χ2 test, p <0.0001) and lower among younger age groups (χ2 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.

Original languageEnglish (US)
Pages (from-to)563-570
Number of pages8
JournalArchives of Medical Research
Volume43
Issue number7
DOIs
StatePublished - Oct 2012

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Pandemics
Mexico
Human Influenza
Hospitalization
Respiratory Tract Infections
Age Distribution
Reproduction
Inpatients
Social Security
Population
Immunity
Age Groups
Demography
Incidence
Growth
Infection

Keywords

  • A/H1N1 influenza pandemic
  • Age distribution
  • Deaths
  • Hospitalizations
  • Transmissibility

ASJC Scopus subject areas

  • Medicine(all)

Cite this

Borja-Aburto, V. H., Chowell, G., Viboud, C., Simonsen, L., Miller, M. A., Grajales-Muñiz, C., ... Echevarría-Zuno, S. (2012). Epidemiological Characterization of a Fourth Wave of Pandemic A/H1N1 Influenza in Mexico, Winter 2011-2012: Age Shift and Severity. Archives of Medical Research, 43(7), 563-570. https://doi.org/10.1016/j.arcmed.2012.09.005

Epidemiological Characterization of a Fourth Wave of Pandemic A/H1N1 Influenza in Mexico, Winter 2011-2012 : Age Shift and Severity. / Borja-Aburto, Víctor H.; Chowell, Gerardo; Viboud, Cécile; Simonsen, Lone; Miller, Mark A.; Grajales-Muñiz, Concepción; González-Bonilla, Cesar R.; Diaz-Quiñonez, Jose A.; Echevarría-Zuno, Santiago.

In: Archives of Medical Research, Vol. 43, No. 7, 10.2012, p. 563-570.

Research output: Contribution to journalArticle

Borja-Aburto, VH, Chowell, G, Viboud, C, Simonsen, L, Miller, MA, Grajales-Muñiz, C, González-Bonilla, CR, Diaz-Quiñonez, JA & Echevarría-Zuno, S 2012, 'Epidemiological Characterization of a Fourth Wave of Pandemic A/H1N1 Influenza in Mexico, Winter 2011-2012: Age Shift and Severity', Archives of Medical Research, vol. 43, no. 7, pp. 563-570. https://doi.org/10.1016/j.arcmed.2012.09.005
Borja-Aburto, Víctor H. ; Chowell, Gerardo ; Viboud, Cécile ; Simonsen, Lone ; Miller, Mark A. ; Grajales-Muñiz, Concepción ; González-Bonilla, Cesar R. ; Diaz-Quiñonez, Jose A. ; Echevarría-Zuno, Santiago. / Epidemiological Characterization of a Fourth Wave of Pandemic A/H1N1 Influenza in Mexico, Winter 2011-2012 : Age Shift and Severity. In: Archives of Medical Research. 2012 ; Vol. 43, No. 7. pp. 563-570.
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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 (χ2 test, p <0.0001) and lower among younger age groups (χ2 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.",
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AU - Chowell, Gerardo

AU - Viboud, Cécile

AU - Simonsen, Lone

AU - Miller, Mark A.

AU - Grajales-Muñiz, Concepción

AU - González-Bonilla, Cesar R.

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KW - Hospitalizations

KW - Transmissibility

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