Abstract
BackgroundThe burden of the pandemic (H1N1) 2009 influenza might be underestimated if detection of the virus is mandated to diagnose infection. Using an alternate approach, we propose that a much higher pandemic burden was experienced in our institution.Methodology/Principal FindingsConsecutive patients (n = 2588) presenting to our hospital with influenza like illness (ILI) or severe acute respiratory infection (SARI) during a 1-year period (May 2009–April 2010) were prospectively recruited and tested for influenza A by real-time RT-PCR. Analysis of weekly trends showed an 11-fold increase in patients presenting with ILI/SARI during the peak pandemic period when compared with the pre-pandemic period and a significant (P<0.001) increase in SARI admissions during the pandemic period (30±15.9 admissions/week) when compared with pre-pandemic (7±2.5) and post-pandemic periods (5±3.8). However, Influenza A was detected in less than one-third of patients with ILI/SARI [699 (27.0%)]; a majority of these (557/699, 79.7%) were Pandemic (H1N1)2009 virus [A/H1N1/09]. An A/H1N1/09 positive test was correlated with shorter symptom duration prior to presentation (p = 0.03). More ILI cases tested positive for A/H1N1/09 when compared with SARI (27.4% vs. 14.6%, P = 0.037). When the entire study population was considered, A/H1N1/09 positivity was associated with lower risk of hospitalization (p<0.0001) and ICU admission (p = 0.013) suggesting mild self-limiting illness in a majority.Conclusion/SignificanceAnalysis of weekly trends of ILI/SARI suggest a higher burden of the pandemic attributable to A/H1N1/09 than estimates assessed by a positive PCR test alone. The study highlights methodological consideration in the estimation of burden of pandemic influenza in developing countries using hospital-based data that may help assess the impact of future outbreaks of respiratory illnesses.
Highlights
The first pandemic of influenza of the 21st century, Pandemic(H1N1)2009 was declared by the WHO on June 11, 2009 [1]
Pandemic influenza was detected more frequently among cases of influenza like illness (ILI) (27.4%) than severe acute respiratory infection (SARI) (14.6%) (p = 0.037)
Detection of viral RNA in respiratory samples as tested by real time RT-PCR, was used as a marker of exposure. In this analysis we found that patients of all age groups presenting with ILI and SARI were infected with A/H1N1/09
Summary
The first pandemic of influenza of the 21st century, Pandemic(H1N1)2009 was declared by the WHO on June 11, 2009 [1]. The first case of the P(H1N1) 2009 in India was reported in May 2009 [6].The establishment of community level person-toperson transmission by July 2009 saw a dramatic increase in persons seeking healthcare. This increased demand for testing along with limited availability of facilities for laboratory diagnosis and management of pandemic influenza, lead to an acute crisis all over the country [7]. Given that previous pandemics of influenza have been associated with a higher burden of morbidity and mortality in developing countries like India [9], we hypothesized that the current pandemic would follow a similar pattern. We propose that a much higher pandemic burden was experienced in our institution
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