MASSACHUSETTS DEPARTMENT OF PUBLIC HEALTH
WEEKLY INFLUENZA UPDATE
September 10, 2009
All data in this report are preliminary and subject to change as more information is received.
New information since last update: H1N1 influenza
As of September 9, 2009, 1,400 confirmed cases of H1N1 have been reported throughout Massachusetts. As of September 3, there have been 9,079 hospitalized cases of H1N1 nationally, with 593[1] deaths.
Table 1. Confirmed H1N1 cases in MA, as of 9/9/09
As shown in Table 1 above, school-aged individuals (5-18 years) have been primarily affected by H1N1, with 63% of cases aged 18 or younger. The median age of cases is 14 and cases have ranged in age from 0 to 84 years. To date, males and females have been equally impacted by H1N1. Overall, 174 cases have been hospitalized (12.4%), which is similar to the national hospitalization rate of 11% as of July 10. In Massachusetts, 11 confirmed H1N1 cases have died. Of the 11 deaths, 8 had underlying conditions. Please note that the number of confirmed cases does not reflect the overall incidence of H1N1 flu because the majority of cases are not tested and are therefore not confirmed (this is true for seasonal flu as well).
Sentinel Provider Surveillance: Influenza-like illness activity
Provider offices across MA report the amount of influenza-like illness (ILI) they see in their patients each week during regular flu season. These doctors’ offices are called “sentinel sites.” Given the unusual occurrence of influenza activity at this time of year, providers throughout the country are continuing to report to their state health departments. Please note that the data do not represent confirmed H1N1 cases, only those with ILI. ILI is defined as fever above 100.0[2] in addition to either cough or sore throat. ILI is a marker of influenza and is used throughout the regular influenza season to monitor influenza since most people are not tested for influenza. Figure 1 indicates that after rising to high levels due to circulating novel H1N1, ILI appears to have returned to normal inter-seasonal levels.
Figure 1: Percentage of ILI visits reported by sentinel provider sites
Please visit the website for the graphic. http://www.cdc.gov/mmwr/pdf/wk/mm58e0910.pdf
Laboratory testing for influenza
The William A. Hinton State Laboratory Institute has been doing confirmatory testing of H1N1 since mid-April, which is typically the late part of the influenza season. The number of ‘confirmed’ cases does not reflect the overall incidence of H1N1 flu because the majority of cases are not tested. This is true for seasonal flu as well. The figure and table below reflect current laboratory data.Figure 2: Laboratory-confirmed (Culture & Rapid Tests) Influenza Cases & Influenza-Like Illness, Massachusetts 2008-2009
Please visit the website for the graphic. http://www.cdc.gov/mmwr/pdf/wk/mm58e0910.pdf
Update: Influenza Activity: United States, April-August 2009
MMWR. Early Release. Vol. 58 / September 10, 2009 http://www.cdc.gov/mmwr/pdf/wk/mm58e0910.pdf
By August, the cumulative number of 2009 pandemic influenza A (H1N1) virus infections in the United States was estimated to be at least 1 million. Pandemic H1N1 activity peaked in the United States during May and June and declined during July and early August. However, during the last 2 weeks of August, activity increased in certain areas of the United States. These recent increases might signal an early start to the 2009–10 influenza season, with pandemic H1N1 influenza viruses predominating at least initially. MMWR. Early Release. Vol. 58 / September 10, 2009
[1] http://www.cdc.gov/h1n1flu/update.htm
[2] Per CDC definition for influenza-like illness: http://www.cdc.gov/h1n1flu/casedef.htm
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