Early Outbreak of 2009 Influenza A (H1N1) in Mexico
Author Information
Author(s): Hsieh Ying-Hen, Ma Stefan, Velasco Hernandez Jorge X., Lee Vernon J., Lim Wei Yen
Primary Institution: China Medical University
Hypothesis
Was there an early epidemic of influenza A (H1N1) in Mexico before the virus was identified?
Conclusion
The study established the existence of an early epidemic in Mexico City and all of Mexico during February/March, indicating that the virus may have already spread to other continents prior to its identification.
Supporting Evidence
- Excess influenza cases were observed during weeks 5-15 in both Mexico City and all of Mexico.
- The estimated basic reproduction number R0 for the early outbreak was 1.59 for Mexico City and 1.25 for all of Mexico.
- The turning point for Mexico City occurred around mid-February, while for all of Mexico it was in early March.
- The study utilized routine influenza surveillance data to establish the early epidemic.
- Findings suggest that the virus may have spread internationally before its identification.
Takeaway
Researchers found that there were more flu cases in Mexico City and all of Mexico earlier than expected, suggesting the flu virus was spreading before it was officially recognized.
Methodology
A mathematical model was fitted to excess laboratory-confirmed influenza cases in Mexico to estimate the transmissibility of the virus.
Potential Biases
The study relies on laboratory confirmed cases, which may not represent the true number of infections due to underreporting.
Limitations
Data was obtained from open sources and is subject to underreporting, complicating the understanding of the early outbreak.
Participant Demographics
The study focused on influenza cases in Mexico City and all of Mexico during early 2009.
Statistical Information
P-Value
1.59 (0.55 to 2.62) for Mexico City; 1.25 (0.76, 1.74) for all of Mexico
Confidence Interval
0.55 to 2.62 for Mexico City; 0.76 to 1.74 for all of Mexico
Statistical Significance
p<0.05
Digital Object Identifier (DOI)
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