Armed Forces Health Surveillance Center DoD Influenza Surveillance Report 2007-2008 Influenza Season Final Report
Synopsis of the 2007-2008 influenza season: • Peak influenza activity occurred during weeks 5-10 for the US overall and most regions. (Figures 1 & 4) • Influenza-like illness (ILI) and Pneumonia and Influenza (P&I) rates were similar among immunized and unimmunized service members for the majority of the weeks. However, during the peak weeks of activity, unimmunized service members had a higher incidence of ILI and P&I compared to the immunized for the overall US. (Figure 1) • The percent of visits for ILI peaked from week 51 to week 2 and then again during weeks 5-9 for the US overall, EUCOM, and PACOM. During weeks 5-9 percents were higher than previous influenza seasons for the US Overall and PACOM region. (Figure 2) • The percent of visits for P&I peaked from week 51 to week 1 and then again during weeks 5-10 for the US overall. In addition, during weeks 5-10, the US overall percents were elevated from previous influenza seasons. For EUCOM and PACOM, the percent of visits for P&I remained relatively steady throughout the season with no distinct peaks in activity. (Figure 3) • 78.4% of the service member influenza RME cases occurred among immunized individuals. • Given the similar incidence rates between immunized and unimmunized individuals for most weeks of the season, but the increased incidence among unimmunized individuals during weeks of peak influenza activity, these results indicate a weak protective effect of the vaccine for this season. Description: The first 3 figures present the weekly data on ILI and P&I events. These figures give an overview of the influenza season by incidence and outpatient visits. This data can give a broad view of the pattern and severity of the season and allow the reader to compare seasonal patterns with previous years, between regions within the U.S., and between the U.S. and international regions. Figures 4 through 6 of this report provide data on influenza reportable medical events by service-specific commands. Incidence of Influenza (Figure 1): Each week the incidence of ILI and P&I are calculated for active duty service members. The numerator comprises the sum of new events occurring during the week of interest and the denominator comprises the total number of persons at risk for that week. Rates are calculated separately by influenza vaccination status at the start of the week. Service members vaccinated against influenza at least 14 days prior to the start of the week are included in the vaccinated group. (Figure 1) Percentage of Outpatient Visits Associated with Influenza (Figures 2 and 3): The percentage of all outpatient visits that have an ILI (Figure 2) or P&I (Figure 3) diagnosis is calculated each week for all service members, regardless of component. Current proportions are graphed against the baseline** and data for the two prior influenza seasons for comparison.
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Figure 1. Incidence Rate of P&I and ILI among Active Duty Service Members
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Figure 2. Percent of All Outpatient Visits with an ILI Diagnosis among all Service Members
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Figure 3. Percent of All Outpatient Visits with a P&I Diagnosis among all Service Members
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Reportable Medical Events: Each week the total number of influenza RME is calculated for service members (including Active, Reserve, and National Guard components) and all other military health system beneficiaries separately. For the service members only, the total number vaccinated at least 14 days prior to the RME date is also reported. Counts for all regions and services are presented in Figure 4. Counts according to Army medical command are presented in Figure 5. Figure 4. RME for Influenza: Confirmed cases (Active Duty (AD) & Reserve Component (RC) vs. Beneficiaries) for All Regions and Services
Figure 5. Army RME for Influenza: Confirmed cases (Active Duty (AD) & Reserve Component (RC) vs. Beneficiaries) by Medical Command
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Background: AFHSC maintains the Defense Medical Surveillance System (DMSS) which is a database containing up-to-date and historical data on medical encounters, vaccinations, and personnel and demographic data about service members from all military services. Using ICD-9 code data for inpatient and outpatient encounters, and influenza vaccination data contained within the DMSS, AFHSC produces weekly summaries of influenza activity among military health system beneficiaries by geographical regions. Two primary outcomes are used for this surveillance: Influenza-like Illness (ILI) and Pneumonia and Influenza (P&I). ILI is defined as a health care encounter that resulted in a diagnostic (ICD-9) code of 79.99, 382.9, 460, 461.9, 465.8, 465.9, 466.0, 486, 487.0, 487.1, 487.8, 490, 780.6, 786.2. P&I is defined as an ICD-9 code of 480-487. AFHSC also receives standardized reports of cases of reportable medical events (RME) from all services. In addition to the Center for Disease Control and Prevention’s Nationally Notifiable Infectious Diseases, additional military specific infections are also captured in the RME system, including Influenza (ICD-9=487). Influenza events that meet a clinical case definition (sudden onset of fever >102.2°F, respiratory systems, myalgia and headache) and are laboratory confirmed are reported as a RME. Regions are defined as New England (Connecticut, Maine, Massachusetts, New Hampshire, Vermont, Rhode Island), Mid Atlantic (New Jersey, New York, Pennsylvania), East North Central (Illinois, Indiana, Michigan, Ohio, Wisconsin), West North Central (Iowa, Kansas, Minnesota, Missouri, Nebraska, North Dakota, South Dakota), South Atlantic (Delaware, Florida, Georgia, Maryland, North Carolina, South Carolina, Virginia, Washington, D.C., West Virginia, US Virgin Islands, Puerto Rico), East South Central (Alabama, Kentucky, Mississippi, Tennessee), West South Central (Arkansas, Louisiana, Oklahoma, Texas), Mountain (Arizona, Colorado, Idaho, Montana, Nevada, New Mexico, Utah, Wyoming), and Pacific (Alaska, California, Hawaii, Oregon, Washington). **For figures 2 and 3, the overall and region baseline is the percentage of outpatient visits for ILI or P&I during non-influenza weeks (weeks 22-39) plus two standard deviations.
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