Characterizing the Epidemiology of the 2009 Influenza A/H1N1 Pandemic in Mexico
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.
:
Please see later in the article for the Editors' Summary
Vyšlo v časopise:
Characterizing the Epidemiology of the 2009 Influenza A/H1N1 Pandemic in Mexico. PLoS Med 8(5): e32767. doi:10.1371/journal.pmed.1000436
Kategorie:
Research Article
prolekare.web.journal.doi_sk:
https://doi.org/10.1371/journal.pmed.1000436
Souhrn
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.
:
Please see later in the article for the Editors' Summary
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