Influenza, 2007

On November 2, 2007, the PHL isolated influenza virus from a Minnesota resident for the first time during the 2007-2008 influenza season. This date represented a slightly early start of influenza activity. Since 1990-1991, the first isolate typically has been between mid-November and mid-December. Influenza activity peaked in late February/early March 2008. 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 1995-1996 influenza season, and a Sentinel Provider Influenza Network was initiated in 1998-1999 to conduct active surveillance. Twenty-eight sentinel sites participated during the 2007-2008 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 ensure sites represent all areas of the state. Clinics are particularly needed in southern region 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 2007-2008 season. Surveillance for influenza-related adult hospitalizations in the metropolitan area was added in 2005 and continued through the 2007-2008 season. From October 1, 2007 to April 26, 2008, 525 adult and pediatric hospitalizations with lab-confirmed influenza were reported to MDH from hospitals in the metropolitan area.

Three pediatric influenza-related deaths were identified during the 2007-2008 influenza season. Two cases were female and one was male. Cases ranged in age from 5 to 12 years. One case was white, non-Hispanic; one case was white, Hispanic; and one case’s race and ethnicity were unknown. Onsets occurred between mid-February and early March 2008. Deaths occurred between late February and mid-March 2008. One case had an underlying health condition. The three cases were not vaccinated for influenza for that season. Two cases resided in the metropolitan area and one resided in Greater Minnesota. During the 2006-2007 season, six pediatric influenza deaths were reported. Prior to 2006-2007, the last reported pediatric influenza death in Minnesota occurred during the 2004-2005 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 2007-2008 season, MDH received reports of probable ILI outbreaks from 135 schools in 44 counties throughout Minnesota and possible outbreaks in 81 schools in 38 counties. A total of 216 schools in 54 counties reported suspected outbreaks in 2007-2008. Since 1988-1989, the number of schools reporting suspected influenza outbreaks has ranged from a low of 38 schools in 20 counties in 1996-1997 to 441 schools in 71 counties in 1991-1992.

An influenza 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 influenza outbreak is confirmed when at least one resident has a positive culture or rapid antigen test for influenza. One hundred fifteen facilities in 48 counties reported confirmed influenza outbreaks in 2007-2008. In all facilities, influenza was laboratory-confirmed by rapid tests or culture. Since 1988-1989, the number of long-term care facilities reporting ILI outbreaks has ranged from a low of six in 1990-1991 to 140 in 2004-2005.

As of May 5, 2008, 189 (22%) of 869 influenza isolates in the PHL were well-matched to one of the three strains included in the vaccine for the 2007-2008 influenza season, compared to approximately 40% nationally. Of those, 55 (29%) were identified as influenza A/H1, 125 (66%) were identified as influenza A/H3, and 7 (4%) were identified as influenza B/Malaysia-like. Four hundred twenty isolates (48%) were identified as influenza B/Shanghai-like, a different lineage than the vaccine reference strain. For 30% of isolates in the PHL, a vaccine match could not be determined; it is likely that many of these isolates were antigenically different from strains included in the 2007-2008 vaccine.

The PHL detected one case of influenza A (H1N1) swine influenza in a 26 year-old female. The case was black, non-Hispanic and lived in the metropolitan area. She had no underlying medical conditions and was not vaccinated for the 2007-2008 influenza season. The identification of this case demonstrates the capacity of the PHL to detect novel influenza viruses.

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 reported on April 8, 2008 that a total of 379 human cases including 239 deaths have been confirmed since January 2003, with an overall case-fatality rate of 63%. Fourteen countries in Asia and Africa have reported human cases of avian influenza. MDH utilizes guidelines developed by the CDC to assess ill patients returning from affected countries. Currently, no cases of h3N1 have been identified in 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.

• For up to date information see>> Influenza (Flu)
  
• Full issue>> Annual Summary of Communicable Diseases Reported to the Minnesota Department of Health, 2007