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Influenza surveillance during the 2001-02 influenza season was conducted in cooperation with the U.S. Centers for Disease Control and Prevention (CDC). Thirty-four Indiana physicians, nurse-managed clinics, emergency departments, immediate care facilities, and university student health centers volunteered to be sentinel physicians/sites. These sentinels were widely distributed throughout Indiana.
Surveillance for the 2001-2002 influenza season began the week ending October 6, 2001, and continued weekly through May 18, 2002. While surveillance was ongoing, the number of patients presenting themselves for influenza-like-illness (ILI) was tracked. For the purpose of surveillance the CDC defines ILI as, "Fever (>100° F [37.8° C] oral or equivalent) and cough or sore throat (in absence of a known cause)." In addition to tracking how many patients presented with ILI, participants reported the total number of patients, broken down by specified age groups. Sentinel sites made weekly reports and submitted them to the repository at the CDC via the Internet, phone, or FAX. Additionally, participants collected nasopharyngeal swabs from patients with ILI whose onset of classic clinical signs started within 72 hours of the appointment. The swabs were then sent to the Indiana State Department of Health (ISDH) Laboratories. The ISDH Laboratory conducted viral isolation and identification of influenza by type and subtype. During the surveillance period, sentinel sites saw 211,363 patients, of which 4,344 sought care for ILI. Figure Inf1 provides a geographical display of the percent of patients seeking care for ILI.
The index (first laboratory confirmed) case occurred during the week ending December 31, 2001. The specimen was typed H3N2 and was obtained from a female resident of Allen County. The percentage of patients seen with ILI did not peak until the CDC week that ended March 11, 2002. Influenza A, H3N2 and H1N1, and Influenza B occurred simultaneously throughout the season. The components in the trivalent influenza vaccine were: A/Moscow/10/99-like, A/New Caledonia/20/99-like, and B/Sichuan. One new Influenza B virus was isolated as B/Hong Kong/330/2001. Two Influenza B isolates were reported and typed as B/Victoria/2/87.
Influenza A and B infections were widely distributed throughout Indiana, but the 2001-2002 season was considered to be mild. Of the 183 influenza cultures from Indiana that were typable by the ISDH Laboratory and the World Health Organization/National Respiratory and Enteric Virus Surveillance System collaborating laboratories, 9 (9.5%) were Influenza A (H1N1), 82 (90%) were Influenza A (H3N2), and 4 (.5%) were identified as Influenza B virus. There were no Influenza C infections identified during the 2001-2002 season.
Age distribution of the patients presenting themselves for treatment of ILI during the 2001-2002 season was similar to the age distribution of previous seasons. Figure Inf2 shows the age distribution for the influenza seasons 1997-2002.