Gerardo Chowell and colleagues address whether school closures and other social
                    distancing strategies were successful in reducing pandemic flu transmission in
                    Mexico by analyzing the age- and state-specific incidence of influenza morbidity
                    and mortality in 32 Mexican states

A Gomez-Gomez

A Valdivia

AC Ghani

AD Langmuir

AJ Valleron

AM Presanis

AR Tuite

AS Monto

B Pourbohloul

BJ Cowling

C Fraser

C Reed

C Viboud

CV Munayco

Cécile Viboud

DL Chao

DR Olson

E McBryde

E Pedroni

FL Dunn

G Ayora-Talavera

G Chowell

Gerardo Chowell

H Nishiura

J Gomez

J Lessler

J Shaman

J Wallinga

J.S. Malik Peiris

JA Cordova-Villalobos

James Tamerius

JF Bishop

JK Louie

JT Wu

LF White

Lone Simonsen

M Lipsitch

MA Miller

Mark A. Miller

MC Bootsma

MG Baker

N Hens

P Hardelid

PY Boelle

R Libster

R Perez-Padilla

S Cauchemez

S Echevarria-Zuno

S Paine

SA Webb

Santiago Echevarría-Zuno

V Andreasen

VA Laguna-Torres

Víctor H. Borja-Aburto

Y Yang

English

PubMed

Background: Mexico’s local and national authorities initiated an intense public health response during the early stages of the 2009 A/H1N1 pandemic. In this study we analyzed the epidemiological patterns of the pandemic during April– December 2009 in Mexico and evaluated the impact of nonmedical interventions, school cycles, and demographic factors on influenza transmission.
Methods and Findings: We used influenza surveillance data compiled by the Mexican Institute for Social Security, representing 40% of the population, to study patterns in influenza-like illness (ILIs) hospitalizations, deaths, and case-fatality rate by pandemic wave and geographical region. We also estimated the reproduction number (R) on the basis of the growth rate of daily cases, and used a transmission model to evaluate the effectiveness of mitigation strategies initiated during the spring pandemic wave. A total of 117,626 ILI cases were identified during April–December 2009, of which 30.6% were tested for influenza, and 23.3% were positive for the influenza A/H1N1 pandemic virus. A three-wave pandemic profile was identified, with an initial wave in April–May (Mexico City area), a second wave in June–July (southeastern states), and a geographically widespread third wave in August–December. The median age of laboratory confirmed ILI cases was ,18 years overall and increased to ,31 years during autumn (p,0.0001). The case-fatality ratio among ILI cases was 1.2% overall, and highest (5.5%) among people over 60 years. The regional R estimates were 1.8–2.1, 1.6–1.9, and 1.2–1.3 for the spring, summer, and fall waves, respectively. We estimate that the 18-day period of mandatory school closures and other social distancing measures implemented in the greater Mexico City area was associated with a 29%–37% reduction in influenza transmission in spring 2009. In addition, an increase in R was observed in late May and early June in the southeast states, after mandatory school suspension resumed and before summer vacation started. State-specific fall pandemic waves began 2–5 weeks after school reopened for the fall term, coinciding with an age shift in influenza cases.
Conclusions: We documented three spatially heterogeneous waves of the 2009 A/H1N1 pandemic virus in Mexico, which were characterized by a relatively young age distribution of cases. Our study highlights the importance of school cycles on the transmission dynamics of this pandemic influenza strain and suggests that school closure and other mitigation measures could be useful to mitigate future influenza pandemics

Chowell, Gerardo

Echevarria-Zuno, Santiago

Viboud, Cecile

Simonsen, Lone

Tamerius, James

Miller, Mark

Borja-Aburto, Victor H.

Georgia State University

Characterizing the Epidemiology of the 2009 Influenza A/H1N1 Pandemic in Mexico

BackgroundMexico's local and national authorities initiated an intense public health response during the early stages of the 2009 A/H1N1 pandemic. In this study we analyzed the epidemiological patterns of the pandemic during April-December 2009 in Mexico and evaluated the impact of nonmedical interventions, school cycles, and demographic factors on influenza transmission.Methods and findingsWe used influenza surveillance data compiled by the Mexican Institute for Social Security, representing 40% of the population, to study patterns in influenza-like illness (ILIs) hospitalizations, deaths, and case-fatality rate by pandemic wave and geographical region. We also estimated the reproduction number (R) on the basis of the growth rate of daily cases, and used a transmission model to evaluate the effectiveness of mitigation strategies initiated during the spring pandemic wave. A total of 117,626 ILI cases were identified during April-December 2009, of which 30.6% were tested for influenza, and 23.3% were positive for the influenza A/H1N1 pandemic virus. A three-wave pandemic profile was identified, with an initial wave in April-May (Mexico City area), a second wave in June-July (southeastern states), and a geographically widespread third wave in August-December. The median age of laboratory confirmed ILI cases was ∼ 18 years overall and increased to ∼ 31 years during autumn (pConclusionsWe documented three spatially heterogeneous waves of the 2009 A/H1N1 pandemic virus in Mexico, which were characterized by a relatively young age distribution of cases. Our study highlights the importance of school cycles on the transmission dynamics of this pandemic influenza strain and suggests that school closure and other mitigation measures could be useful to mitigate future influenza pandemics. Please see later in the article for the Editors' Summary

Mark A Miller

Víctor H Borja-Aburto

Directory of Open Access Journals

PLoS Medicine

Characterizing the epidemiology of the 2009 influenza A/H1N1 pandemic in Mexico.

Crossref

Background: Mexico’s local and national authorities initiated an intense public health response during the early stages of the 2009 A/H1N1 pandemic. In this study we analyzed the epidemiological patterns of the pandemic during April– December 2009 in Mexico and evaluated the impact of nonmedical interventions, school cycles, and demographic factors on influenza transmission.
Methods and Findings: We used influenza surveillance data compiled by the Mexican Institute for Social Security, representing 40% of the population, to study patterns in influenza-like illness (ILIs) hospitalizations, deaths, and case-fatality rate by pandemic wave and geographical region. We also estimated the reproduction number (R) on the basis of the growth rate of daily cases, and used a transmission model to evaluate the effectiveness of mitigation strategies initiated during the spring pandemic wave. A total of 117,626 ILI cases were identified during April–December 2009, of which 30.6% were tested for influenza, and 23.3% were positive for the influenza A/H1N1 pandemic virus. A three-wave pandemic profile was identified, with an initial wave in April–May (Mexico City area), a second wave in June–July (southeastern states), and a geographically widespread third wave in August–December. The median age of laboratory confirmed ILI cases was ,18 years overall and increased to ,31 years during autumn (p,0.0001). The case-fatality ratio among ILI cases was 1.2% overall, and highest (5.5%) among people over 60 years. The regional R estimates were 1.8–2.1, 1.6–1.9, and 1.2–1.3 for the spring, summer, and fall waves, respectively. We estimate that the 18-day period of mandatory school closures and other social distancing measures implemented in the greater Mexico City area was associated with a 29%–37% reduction in influenza transmission in spring 2009. In addition, an increase in R was observed in late May and early June in the southeast states, after mandatory school suspension resumed and before summer vacation started. State-specific fall pandemic waves began 2–5 weeks after school reopened for the fall term, coinciding with an age shift in influenza cases.
Conclusions: We documented three spatially heterogeneous waves of the 2009 A/H1N1 pandemic virus in Mexico, which were characterized by a relatively young age distribution of cases. Our study highlights the importance of school cycles on the transmission dynamics of this pandemic influenza strain and suggests that school closure and other mitigation measures could be useful to mitigate future influenza pandemics.Originally published in:
Chowell G, Echevarría-Zuno S, Viboud C, Simonsen L, Tamerius J, Miller MA, et al. (2011) Characterizing the Epidemiology of the 2009 Influenza A/H1N1 Pandemic in Mexico. PLoS Med 8(5): e1000436. doi:10.1371/journal.pmed.1000436</p

ScholarWorks @ Georgia State University

Mexico's local and national authorities initiated an intense public
                        health response during the early stages of the 2009 A/H1N1 pandemic. In this
                        study we analyzed the epidemiological patterns of the pandemic during
                        April–December 2009 in Mexico and evaluated the impact of nonmedical
                        interventions, school cycles, and demographic factors on influenza
                        transmission.<0.0001). The case-fatality ratio among
                        ILI cases was 1.2% overall, and highest (5.5%) among people
                        over 60 years. The regional R estimates were 1.8–2.1, 1.6–1.9,
                        and 1.2–1.3 for the spring, summer, and fall waves, respectively. We
                        estimate that the 18-day period of mandatory school closures and other
                        social distancing measures implemented in the greater Mexico City area was
                        associated with a 29%–37% reduction in influenza
                        transmission in spring 2009. In addition, an increase in R was observed in
                        late May and early June in the southeast states, after mandatory school
                        suspension resumed and before summer vacation started. State-specific fall
                        pandemic waves began 2–5 weeks after school reopened for the fall
                        term, coinciding with an age shift in influenza cases.We documented three spatially heterogeneous waves of the 2009 A/H1N1 pandemic
                        virus in Mexico, which were characterized by a relatively young age
                        distribution of cases. Our study highlights the importance of school cycles
                        on the transmission dynamics of this pandemic influenza strain and suggests
                        that school closure and other mitigation measures could be useful to
                        mitigate future influenza pandemics.
                   

Chowell Gerardo

Echevarría-Zuno Santiago

Viboud Cécile

Simonsen Lone

Tamerius James

Miller Mark A.

Borja-Aburto Víctor H.

Public Library of Science (PLOS)

Characterizing the Epidemiology of the 2009 Influenza A/H1N1 Pandemic
                    in Mexico

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Characterizing the Epidemiology of the 2009 Influenza A/H1N1 Pandemic in Mexico

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