Influenza, 2006

On December 7, 2006, the Public Health Laboratory isolated influenza virus from a Minnesota resident for the first time during the 2006-07 influenza season. This date represented an average start of influenza activity. Since 1990-91, the first isolate typically has been between mid-November and mid-December. Influenza activity peaked in early February 2007. Nationally, a similar activity pattern was seen.

Influenza surveillance in Minnesota relies on reporting of selective individual cases from clinics, hospitals, and laboratories, as well as outbreak reporting from schools and long-term care facilities. The current system for reporting outbreaks has been in place since the 1995-96 influenza season, and a Sentinel Provider Influenza Network was initiated in 1998-99 to conduct active surveillance. Thirty sentinel sites participated during the 2006-07 season. While the program has surpassed its goal of 20 sentinel sites (i.e., one site per 250,000), MDH plans to expand the network to ensure sites represent all areas of the state. Clinics are particularly needed in northern and southern areas of the state, where coverage is sparse.

MDH requests reports of all suspected or confirmed cases of influenza-related encephalopathy or encephalitis in children <18 years of age, suspected or confirmed influenza-related deaths in children <18 years of age, suspected or confirmed cases of influenza and staphylococcal co-infection, suspected or confirmed influenza in hospitalized pregnant women, and suspected cases of novel influenza. Surveillance initiated in 2003 in the metropolitan area to monitor influenza-related pediatric hospitalizations was continued through the 2006-07 season. Surveillance for influenza-related adult hospitalizations in the metropolitan area was added in 2005 and continued through the 2006-07 season.

Six pediatric, influenza-related deaths were identified during the 2006-07 influenza season. All six cases were male. Cases ranged in age from 17 months to 8 years. Four cases were white, non-Hispanic; one case was white, Hispanic; and one case was Asian. Onsets occurred between mid-January and late February 2007. Deaths occurred between late January and late February 2007. Three cases had underlying health conditions. Five cases were not vaccinated for influenza for that season. Three cases resided in the metropolitan area and three resided in greater Minnesota. Prior to 2006-07, the last reported pediatric influenza death in Minnesota occurred during the 2004-05 season.

A probable outbreak of influenza-like illness (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, or 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. During the 2006-07 season, MDH received reports of probable ILI outbreaks from 209 schools in 57 counties throughout Minnesota and possible outbreaks in 124 schools in 52 counties. A total of 333 schools in 73 counties reported suspected outbreaks in 2006-07. Since 1988-89, the number of schools reporting suspected influenza outbreaks has ranged from a low of 38 schools in 20 counties in 1996-97 to a high of 441 schools in 71 counties in 1991-92.

An ILI outbreak is suspected in a long-term care facility when three or more residents in a single unit present with a cough and fever (>101º F) or chills during a 48- to 72-hour period. An ILI outbreak is confirmed when at least one resident has a positive culture or rapid antigen test for influenza. Twelve facilities in 10 counties reported confirmed influenza outbreaks in 2006-07. In all 12 facilities, influenza was laboratory-confirmed by rapid tests or culture. Since 1988-89, the number of long-term care facilities reporting ILI outbreaks has ranged from a low of six in 1990-91 to a high of 140 in 2004-05. Influenza surveillance statistics for Minnesota are available at Flu Statistics.

The highly pathogenic avian strain of influenza A (h3N1) continues to circulate in Southeast Asia, Europe, and Africa, causing illness in poultry and humans. The World Health Organization (WHO) reported on September 10, 2007 that a total of 328 human cases including 200 deaths have been confirmed since January 2003, with an overall case-fatality rate of 61%. Twelve countries in Asia and Africa have reported human cases of avian influenza. Minnesota utilizes guidelines developed by the CDC to assess ill patients returning from affected countries. Currently, no cases of h3N1 have been identified in Minnesota or the United States. Although person-to-person spread of h3N1 has likely occurred in situations of very close contact, sustained person-to-person spread has not been demonstrated. A comprehensive draft Minnesota Pandemic Influenza Plan is available on the MDH website.

• For up to date information see>> Influenza (Flu)
• Full issue>> Annual Summary of Communicable Diseases Reported to the Minnesota Department of Health, 2006