# 5038
A detailed epidemiological study appears today in the CMAJ that looks at the differences between the first (April-August) and second waves (Sept-April 2010) of the 2009 H1N1 pandemic.
Admittedly, this is a data-heavy report, and the details are probably of most interest to epidemiologists, policy planners, and clinicians.
Melissa Helferty, Julie Vachon, Jill Tarasuk , Rachel Rodin, John Spika, Louise Pelletier
Abstract (Excerpts)
Results: A total of 8678 hospital admissions (including 1473 ICU admissions) and 428 deaths related to pandemic (H1N1) influenza were report ed during the pandemic and post-peak period. There were 4.8 times more hospital admissions, 4.0 times more ICU admissions and 4.6 times more deaths in the second pandemic wave than in the first wave. ICU admissions and deaths as a proportion of hospital admissions declined in the second wave; there was a 16% proportional decline in ICU admissions and a 6% proportional decline in deaths compared with the first wave. Compared with patients admitted to hospital in the first wave, those admitted in the second wave were older (median age 30 v. 23 years) and more had underlying conditions (59.7% v. 47.5%). Pregnant women and Aboriginal people accounted for proportionally fewer patients who were admitted to hospital or who died in the second wave than in the first.
Interpretation: The epidemiologic features of the first and second waves of the 2009 pandemic differed. The second wave was substantially larger and, although the patients admitted to hospital were older and more of them had underlying conditions, a smaller proportion had a severe outcome.
The full report is available at this link but some of the highlights include:
- In terms of the number of cases, the second wave was substantially larger than the first and saw more deaths and more hospitalizations
- But the percentage of deaths and severe infections among those hospitalized was lower in the second wave
- While all age groups saw increases in hospitalizations during the second wave, adults aged (45-64) saw the greatest increase, and school aged children (5-19) saw the smallest increase.
- Pregnant women and aboriginal people were disproportionately affected during the duration of the pandemic, but more so during the first wave than the second.
- The proportion of patients with underlying medical conditions increased during the second wave.
The authors credit public health measures and clinical interventions implemented between the first and second waves for the reductions in the percentage of severe cases.
For a more general overview, the Vancouver Sun has a report:
2nd wave of H1N1 pandemic led to more hospitalizations, deaths: Report
By Carmen Chai, Postmedia News November 8, 2010
