Influenza, 2005

The Public Health Laboratory isolated influenza for the first time of the 2005-6 influenza season from a Minnesota resident on December 5, 2005, which represented an average start of activity. Since 1990-91, the first isolate typically has been between mid-November and mid-December. Influenza activity was sporadic in Minnesota until mid-January and didn’t peak until the second week in March. A similar activity pattern was seen nationally.

Influenza surveillance 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. Twenty-seven sentinel sites participated during the 2005-6 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 northern and southern areas of the state where coverage is sparse.

In response to increasing influenza- related encephalitis cases in children in Japan and reports of severe influenza in pregnant women in the United States, enhanced influenza surveillance was implemented during the 2003-4 influenza season and has continued through the 2005-6 season. MDH requested reports of 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 Twin Cities metropolitan area to monitor influenza-related pediatric hospitalizations was also continued through the 2005-6 season.

No pediatric, influenza-related deaths were identified during the 2005-6 influenza season. Two cases of influenza-related encephalopathy were identified. These included a 10-year-old male of unknown race with history of renal disease, and an 18-year-old Asian male with no known underlying medical conditions. Onsets occurred in March 2006 and November 2005, respectively.

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, 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 2005-6 season, MDH received reports of probable ILI outbreaks from 116 schools in 40 counties throughout Minnesota and possible outbreaks in 81 schools in 30 counties. 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. Fifty facilities in 20 counties reported confirmed or suspected ILI outbreaks in 2005-6. In all 50 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 1990-91 to a high of 140 in 2004-5.

The highly pathogenic avian strain of influenza A (h3N1) continues to circulate in Southeast Asia while expanding to areas of Europe and Africa, causing illness in poultry and humans. The World Health Organization (WHO) reported on June 6, 2006 that a total of 225 human cases including 128 deaths have been confirmed since January 2003, with an overall case-fatality rate of 57%. Ten 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.

• For up to date information see>> Influenza (Flu)
• Full issue>> Annual Summary of Communicable Diseases Reported to the Minnesota Department of Health, 2005