Currently, there are 7.84 million veterans enrolled and 5.58 million who received healthcare in the VA system in 2008 at 153 VA medical facilities plus community-based outpatient clinics (CBOCs) in all 50 states, Puerto Rico, U.S. Virgin Islands, Guam, American Samoa, and the Philippines
. For the 2008–09 influenza season extending to week 30 (ending August 1, 2009), 633,893 unique veteran patients had approximately 694,574 visits with an ILI diagnoses reported in VA ESSENCE. A comparison of the percentage of VA visits for ILI each week was calculated and compared to the CDC's ILINet (). Visits in the VA occurred in a similar pattern to ILINet with peaks in late December and early February. Initially, the VA had a higher percentage of visits for ILI than ILINet providers, however, from week 3 onward the overall percentage of visits for ILI in the VA were lower than reported by the ILINet. Small peaks in February and late April/early May were present, mirroring the ILINet data; however, the peaks observed in VA were flatter and smaller.
VA ILI cases compared to CDC ILINet from Sept. 28, 2008-July 31, 2009 (corresponding to CDC 2008–2009 flu season weeks 40–30).
Visits for ILI from all VA facilities nationwide detected using VA ESSENCE from Sept. 28, 2008 to July 31, 2009 are shown in with the early period of pandemic H1N1 2009 displayed in . The saw-tooth pattern seen as regular drops in counts are due to weekend variation since the majority of VA clinics are closed on weekends and visits recorded on weekends are primarily from ED visits. The ESSENCE detecting algorithms are designed to account for this weekend variation. A similar depiction of all VA outpatient visits coded with an ICD-9-CM code specific for influenza (487), but not necessarily confirmed influenza-positive cases, from Sept. 28, 2008 to July 31, 2009 is seen in with the early period of pandemic H1N1 2009 demonstrated in . Red alerts (indicating a significant elevation in the number of influenza-coded visits in the system) were seen at the beginning of the influenza season as well as during the emergence of pandemic H1N1 2009 in late April/early May.
VA Outpatient Visits for ILI from the ESSENCE Surveillance System, Sept 28, 2008-July 31, 2009 (corresponding to CDC 2008–2009 flu season weeks 40–30).
VA Outpatient Visits with Influenza (ICD-9-CM 487) from ESSENCE, Sept. 28, 2008-July 31, 2009 (corresponding to CDC 2008–2009 flu season weeks 40–30).
The frequency of each ICD-9-CM code was extracted from VA ESSENCE (). The top three ILI ICD-9-CM codes during the 2008–09 seasonal influenza period (Sept. 28, 2008-April 25, 2009 corresponding to CDC 2008–2009 flu season weeks 40–16) were acute upper respiratory infection (URI) NOS (465.9, 24%), cough (786.2, 20%), and acute bronchitis (466.0, 14%). The pandemic H1N1 2009 outbreak started in the VA on April 26, 2009 with the first confirmed case and was detected as an emergence of red alerts for the ILI syndrome group (). During the early pandemic H1N1 2009 period (April 26, 2009-July 31, 2009 corresponding to CDC 2008–2009 flu season weeks 17–30), the most common codes utilized were cough (786.2, 25%), acute upper respiratory infection (URI) NOS (465.9, 20%), and pneumonia, organism NOS (486, 13%). The ILI subgroups were similar for both time periods with the three most common being URI, acute bronchitis and cough ().
Frequencies for 17 of the 31 codes significantly changed after the start of pandemic H1N1 2009 at VA facilities (). Six of 17 significantly decreased during the early pandemic H1N1 2009 period while 11 significantly increased during that time (). Several of the codes which significantly increased during the early pandemic H1N1 2009 period included symptoms such as cough (786.2) [OR 1.3, p<1.00×10−7, CI 1.28–1.31], throat pain (784.1) [OR 1.45, p<1.00×10−7, CI 1.36–1.54], fever (780.6/780.60) [OR 1.71, p<1.00×10−7, CI 1.68–1.77], and chills (780.64) [OR 1.34, p<1.00×10−6, CI 1.20–1.49]. In addition, an increase in influenza with pneumonia (487.0) [OR 1.69, p<0.01, CI 1.11–2.57] and influenza with other manifestations (487.8) [OR 3.4, p<1.00×10−7, CI 2.16–5.37] was seen despite these remaining an overall low percentage of ILI-related visits and a decrease in the code for influenza with respiratory manifestation NEC (487.1) [OR 0.68, p<1.00×10−7, CI 0.65–0.72] during the early pandemic H1N1 2009 period. Interestingly, influenza with respiratory manifestation NEC (487.1) was used significantly less during the early period of the pandemic H1N1 2009 outbreak, however, it was the most common code used among the first 150 confirmed pandemic H1N1 2009 VA cases (61/150, 41%). Other ICD-9-CM codes used in confirmed cases include acute URI NOS (465.9) [39/150, 26%], fever (780.6) [19/150, 13%], pneumonia, organism NOS (486) [18/150, 12%], cough (786.2) [18/150, 12%], viral infection NOS (079.99) [9/150, 6%], acute bronchitis (466) [8/150, 5%], bronchitis NOS (490) [4/150, 3%], influenza with pneumonia (487.0) [3/150, 2%], acute pharyngitis (462) [3/150, 2%], and acute nasopharyngitis (460) [1/150, 0.7%] (). Of importance, the 150 confirmed-positive pandemic H1N1 2009 cases were not uniformly coded as influenza and only the above 11 of the 31 defined ILI codes were utilized. Of the confirmed pandemic H1N1 2009 cases, 136/150 (90.7%) were captured in the ILI syndrome group in VA ESSENCE. Seven of the 14 that were not detected in VA ESSENCE were coded with ICD-9-CM codes that were outside of the ILI syndrome group. Six of the 14 patients not captured in VA ESSENCE were employees seen in a VA occupational health clinic that are not regularly detected in the system. One of the 14 patients was directly admitted and was not seen in the outpatient or emergency department setting.
ICD-9-CM codes that significantly changed since the start of pandemic H1N1 2009.
ICD-9-CM Codes used for laboratory-confirmed pandemic H1N1 2009 cases in VA facilities.