Influenza, 2004

On October 5, 2004, MDH received notice that half of the influenza vaccine expected for the upcoming season would not be available. This prompted immediate public health action to determine the vaccine supply in Minnesota and redistribute it to reach groups most at risk for complications of influenza. As a result of public health efforts, as well as private providers, vaccine was made available to all Minnesota long-term care facility residents by early November 2004.

The Public Health Laboratory isolated influenza for the first time of the 20045 influenza season from a Minnesota resident on October 18, 2004, which represented an early start of activity. Since 1990-91, the first isolate typically has been between mid-November and mid-December. Despite the early isolation, influenza activity was sporadic in Minnesota until mid-December and didn’t peak until the first week in February. 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. Twenty-eight sentinel sites participated during the 2004-5 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 continued through the 2004-5 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 metropolitan area to monitor influenza-related pediatric hospitalizations was also continued through the 2004-5 season.

Two cases of influenza-related encephalopathy and one pediatric, influenza-related death were identified in 2004-5. The encephalopathy cases presented in a 14-year-old and a 4-year-old. The 14-year-old had no preexisting conditions, and the 4-year-old had a history of pneumonia, diabetes, and gastroesophageal reflux. Onsets of symptoms in the two were in mid-December and early January; both resulted in mild neurologic sequelae. The pediatric death occurred in a 6-year-old from Otter Tail County. The child had a co-infection of group A streptococcus and influenza B with no history of current influenza vaccination. The patient presented to a hospital emergency department in March in full respiratory arrest; resuscitation efforts were unsuccessful.

The Public Health Laboratory received 820 influenza specimens for viral confirmation and strain identification. Of these isolates, 535 (65%) were influenza type A/Wyoming like (H3); 273 (33%) were B/Sichuan-like; 9 (1%) were A; two (< 1%) were B/Hong Kong like, and one (< 1%) was B. Influenza A/California/7/2004-like (H3N2), which was not included in the 2004-5 vaccine, was the predominant strain circulating nationally, representing 72% of influenza A viruses typed at CDC. In Minnesota, there were no cases of influenza A/California/7/2004-like identified this past season, and all of the circulating strains were well matched to the vaccine components. Studies conducted during previous seasons with imperfect vaccine matches have shown that even a poorly matched vaccine is still moderately effective in preventing influenza-related hospitalizations and deaths.

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 2004-5 season, MDH received reports of probable ILI outbreaks from 155 schools in 48 counties throughout Minnesota and possible outbreaks in 101 schools in 44 counties. Since 1988-89, the number of schools reporting suspected influenza outbreaks has ranged from 38 schools in 20 counties in 1996-97 to 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. The number of long-term care facilities reporting outbreaks this season was particularly high. One hundred forty facilities in 54 counties reported confirmed or suspected ILI outbreaks in 2004-5. In all 140 facilities, influenza was laboratory-confirmed by rapid tests or culture. In comparison, 44 long-term care facilities reported outbreaks during the 2003-4 season. Since 1988-1989, the number of long-term care facilities reporting ILI outbreaks has ranged from six in 199091 to 79 in 1997-98.

The highly pathogenic avian strain of influenza A (h3N1) continues to circulate in Southeast Asia and cause illness in poultry and humans. The World Health Organization (WHO) reported on July 27, 2005 that a total of 109 human cases including 55 deaths have been confirmed since January 2004, with an overall case-fatality rate of 51%. These confirmed cases have been identified in Thailand, Vietnam, and Cambodia. Collective surveillance efforts from WHO, the CDC, as well as health authorities from Southeast Asia and around the world are in place to attempt to identify new cases and prevent spread. 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. h3N1 has not definitively demonstrated person-to-person spread, but in May 2005, WHO reported that the virus showed evidence of becoming more transmissible, though less virulent. It is possible that this change could make widespread global transmission of h3N1 more likely. Pandemic influenza planning has intensified at global, national, and state levels in the past year as the threat of h3N1 increases.

In April 2005, it was discovered that U.S. laboratories including some in Minnesota had inadvertently received proficiency samples containing the H2N2 influenza strain, which has not circulated in humans since 1969. H2N2 was the strain responsible for causing the 1957 pandemic. The CDC and agencies that sent out the samples provided instructions to immediately destroy any remaining samples. MDH followed up with all Minnesota laboratories to ensure that the samples had been destroyed.

The events of the 2004-5 influenza season highlight the need for coordinated efforts between public and private health care to manage influenza. Vaccination of high-risk individuals for seasonal influenza, surveillance for novel virus strains, and planning efforts for an influenza pandemic are all important strategies to increase our capacity to effectively deal with influenza.

• For up to date information see>> Influenza (Flu)
• Full issue>> Annual Summary of Communicable Diseases Reported to the Minnesota Department of Health, 2004