EPI UPDATE

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In this issue:

1. Influenza Surveillance

2. Summary report: Influenza activity in Florida, 2001-2002 season.

Carina Blackmore, M.S., Vet Med, PhD. Bureau of Epidemiology

The influenza season in Florida may begin as early as October. For that reason, we are highlighting influenza surveillance in this special edition of the Epi-Udate.

Each year influenza viruses cause significant morbidity and mortality in Florida. To better monitor the disease in our state the Florida Department of Health has for the past 6 years coordinated a voluntary influenza sentinel physician surveillance network. Other goals for this program are: (1) to monitor the antigenic changes of circulating virus strains (2) develop a surveillance system that will provide an early warning and adequate monitoring capabilities in the setting of the next influenza pandemic and (3) provide medical practitioners and other Florida residents with current and accurate information regarding the incidence and severity of the disease in our state.

The Florida Influenza Sentinel Physician Surveillance Network is part of a national influenza surveillance network coordinated by the Centers for Disease Control and Prevention (CDC). The program has two components: 1. Participating primary care providers report the number of patients diagnosed with influenza-like illness weekly to CDC either via the internet or by telephone. 2. They also submit laboratory specimens for influenza virus isolation and strain typing, free of charge, to the Florida Department of Health Bureau of Laboratories. All participants will receive weekly updates on the clinical and laboratory influenza surveillance results free of charge through our newsletter, the Epi Update, and the CDC’S MMWR (a subscription valued at $130.00). Participants will also receive a free subscription to the journal Emerging Infectious Diseases.

We are currently looking for additional physicians who are willing to help us monitor influenza activity in the general population during the 2002-2003 season. Last year we had 65 participants in this important surveillance program but our ultimate goal is to have 70 sentinel physicians across Florida.

The statewide influenza surveillance coordinator is Dr. Carina Blackmore. Please don’t hesitate to call her at (904) 791-1744 or your local health department if you have questions regarding this year’s surveillance program.

Like the 2000-2001 influenza season, the 2001-2002 influenza season was mild in Florida. Three hundred seventy four viral specimens were cultured for respiratory viruses in our state laboratories this year, almost identical to the number of specimens processed last season (n=369). During the 1999-2000 season, the state laboratories received 522 respiratory culture requests. Of the 375 cultures, 144 (38%) were positive for influenza. The vast majority of the isolates typed this season were influenza A (H3N2) (93%), although increased influenza B activity was detected during March and April, 2002 (Figure 1). Only 3 isolates of influenza A (H1N1) were detected this year.

The percentage of reported influenza-like illness (ILI) patient visits to physicians participating in the Florida Influenza Sentinel Physicians Surveillance Network (FISPSN) remained low throughout the year. Virus activity peaked in late January when 83% of specimens submitted to the state lab tested positive for influenza and 2.7 percent of FISPSN patients sought medical care for ILI (Figure 2). Last season influenza activity peaked in early January when 5% of patients sought care for ILI.

Sixty-five clinics in 27 Florida counties participated in the influenza sentinel surveillance network this year, a 20% improvement from last year. The goal of this program is to have one sentinel physician reporting ILI/ 250,000 Florida residents. This is the first year since the Florida Department of Health started the program in 1998, we have been able to reach this goal.

Two outbreaks of influenza were reported to the state health office this year; one community based outbreak affecting young children in Pinellas and other Tampa Bay area counties and one nursing home outbreak in Sarasota county (see attached report).

The overall nationwide influenza activity peaked in mid-late February 2002 when 25.9% of the respiratory specimens submitted to WHO and NERVSS laboratories tested positive for influenza and 3.5% of patient visits to sentinel physicians were due to ILI. During the past 3 seasons, the peak percentages of respiratory specimens positive for influenza viruses have ranged from 24% to 33% and the peak percentages for ILI visits has ranged between 4% and 6%.

Based on genetic testing of virus strains CDC concluded that by and large, the 2000-2001 influenza vaccine strains were well matched to circulating virus strains. Circulating influenza A virus strains were very similar to this years vaccine strains. For this reason, influenza A/H1N1/New Caledonia and influenza A/H3N2/Moscow will remain the influenza A components of the 2002-2003 years vaccine. However, influenza B viruses currently circulating belong to two antigencally distinct lineages, B/Yamagata and B/Victoria. The B component of the current influenza vaccine belongs to the B/Yamagata lineage. B/Victoria like viruses had not been identified outside of Asia since 1991 but in the last few months they have, yet again, spread across the world. B/Victoria will replace the B/ Sichuan strain as the influenza B component in the 2002-2003 influenza vaccine.

The national influenza surveillance program runs from October 1 to May 20 each year.

Update: Influenza Activity --- United States and Worldwide, 2000--01 Season, and Composition of the 2001--02 Influenza Vaccine. MMWR, June 8, 2001, 50, 466-470.

Prevention and Control of Influenza Recommendations of the Advisory Committee on Immunizations Practices (ACIP), MMWR, April 12, 2002, 51 / RR-3.