Influenza, 2002

The MDH Public Health Laboratory confirmed the first influenza isolate of the 2002-2003 influenza season in Minnesota on December 30, 2002, which represented a slight delay in the usual start of influenza activity. Since 1990-1991, the first influenza isolate typically has been identified between mid-November and mid-December. Influenza activity nationally and in states surrounding Minnesota peaked during the first week in February, whereas influenza activity in Minnesota began slowly and peaked during the first week in March. Deaths attributable to influenza and pneumonia in Minnesota did not exceed the epidemic threshold during the 2002-2003 influenza season.

Influenza surveillance in Minnesota relies on reporting of individual cases from clinics, hospitals, and laboratories, as well as outbreak reporting from schools and long-term care facilities. The current surveillance systems for reporting outbreaks in schools and long-term care facilities have been in place since the 1995-1996 influenza season, and a Sentinel Physician Influenza Network was initiated in 1998-1999 to conduct active surveillance. Twenty-two sentinel sites participated in the network during the 2002-2003 season. While the program has surpassed its goal of 20 sentinel sites (i.e., one site per 250,000 population), MDH plans to expand the network to include active surveillance sites in all areas of the state. In order to establish baseline rates of influenzalike illness (ILI) and to monitor influenza year-round, MDH initiated a Summer Influenza Sentinel Surveillance program with 15 participating sites in May 2002.

The MDH Public Health Laboratory received 523 influenza isolates for viral confirmation and strain identification. Of these isolates, 279 (53%) were influenza type A/Panama-like (H3N2); 162 (31%) were A/New Caledonia (H1N1); 72 (14%) were influenza B/ Hong Kong; two (<1%) were B/ Sichuan-like; four (1%) were influenza A (with unidentifiable strains); and four (1%) were influenza type B (with unidentifiable strains). Influenza type A/Panama, A/New Caledonia, and B/ Hong Kong also were the predominant strains circulating nationally. The predominant influenza strains circulating in Minnesota during 2002-2003 were well matched to the strains in the influenza vaccine used in 2002-2003. Of the two influenza B stains identified in Minnesota, only B/Hong Kong was included in the vaccine, which includes only one influenza B strain each year.

A probable outbreak of ILI in a school is defined as a doubled absence rate with all of the following primary influenza symptoms reported among students: rapid onset, fever of >101º F, illness lasting 3 or more days, and at least one secondary influenza symptom (e.g., myalgia, headache, cough, coryza, sore throat, chills). A possible ILI outbreak in a school is defined as a doubled absence rate with reported symptoms among students including two of the primary influenza symptoms and at least one secondary influenza symptom. In 2002-2003, MDH received reports of probable ILI outbreaks from 151 schools in 43 counties throughout Minnesota and possible outbreaks in 96 schools in 38 counties. Schools began reporting ILI outbreaks in mid-November; over half of the probable and possible ILI outbreaks were reported during February. Since 1988-1989, the number of schools reporting suspected influenza outbreaks has ranged from 38 schools in 20 counties in 1996- 1997 to 441 schools in 71 counties in 1991-1992.

An ILI outbreak is suspected in a longterm care facility when three or more residents in a single unit present with a cough and fever (>101º F) or chills during a period of 48 to 72 hours. An ILI outbreak is confirmed when at least one resident has a positive culture or rapid-antigen test for influenza. Thirty-three long-term care facilities reported confirmed or suspected ILI outbreaks in 2002-2003. In 26 (79%) of these facilities, influenza was laboratoryconfirmed by rapid tests or culture. Fourteen (42%) facilities reported outbreaks between mid-February and mid-March. Since 1988-1989, the number of long-term care facilities reporting ILI outbreaks has ranged from six in 1990-1991 to 79 in 1997- 1998.

International influenza surveillance efforts identified two different avian strains of influenza in humans during 2002-2003. Two Hong Kong residents (a 33-year-old father and 9-year-old son) traveling in Fujian Province, China were infected with an influenza A (h3N1) strain in early February. The father died 9 days after onset of illness, while the son recovered. Other family members suffered from ILI, including an 8-year-old sibling who died; h3N1 was not isolated in this case. No additional spread of h3N1 was detected. At the end of February 2003, the Netherlands began reporting outbreaks of influenza A (H7N7) in poultry and swine on several farms. As of April 25, 2003, 83 confirmed cases of human H7N7 had been reported in the Netherlands. Conjunctivitis was the most common presenting symptom among these cases (79 cases, 95%); six cases with conjunctivitis also reported mild ILI, one case had ILI only, and two cases could not be classified. In addition to these cases, a 57-year-old veterinarian who visited an affected farm in April died in mid-April due to acute respiratory distress syndrome and related complications from an H7N7 infection. Evidence of person-to-person transmission from two poultry workers to three family members was documented.

Sustained person-to-person transmission is a precursor to a pandemic influenza event. The identification of these avian strains in humans further emphasizes the importance of collecting specimens for viral cultures as part of influenza surveillance and pandemic influenza preparedness.

• For up to date information see>> Influenza (Flu)
• Full issue>> Annual Summary of Communicable Diseases Reported to the Minnesota Department of Health, 2002