Influenza, 2003

The MDH Public Health Laboratory confirmed the first influenza isolate of the 2003-2004 influenza season in Minnesota on November 12, 2003, which represented an early start of influenza activity. Since 1990-1991, the first influenza isolate typically has been identified between mid-November and mid-December. Increased influenza activity followed shortly thereafter, both nationally and locally. During the week of November 22, 10 states reported widespread influenza activity. Reports from other states of severe influenza illness and deaths in children were making news headlines, causing increased public demand for vaccine and quickly exhausting the existing vaccine supply. More than 5,000 phone calls were made to an MDH influenza vaccine hotline between December 5 and 16, requesting information on vaccine availability. National influenzalike illness (ILI) activity peaked the week of December 20, and peaked in Minnesota the following week.

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 Provider Influenza Network was initiated in 1998-1999 to conduct active surveillance. Twenty-nine sentinel sites participated in the network during the 2003-2004 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 active surveillance sites represent all areas of the state. Volunteers are particularly needed in northern and southern areas of the state where there is sparse sentinel coverage. In order to establish baseline rates of ILI and to monitor influenza year-round, MDH initiated a Summer Influenza Sentinel Surveillance program with 17 participating sites in May 2003.

In response to increasing influenza-related encephalitis cases in children in Japan and reports of severe influenza in pregnant women in the southern United States, enhanced surveillance was implemented during the 2003-2004 influenza 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, and suspected or confirmed influenza in hospitalized pregnant women. A surveillance project was also initiated in the metropolitan area to monitor influenza-related pediatric hospitalizations.

As a result of enhanced surveillance, two cases of influenza-related encephalopathy and one pediatric, influenza-related death were identified. The encephalopathy cases presented in a six-month-old from Martin County and a four-year-old from Faribault County. The six-month-old had no preexisting conditions and was not vaccinated for influenza. The four-year-old had a history of pneumonia as a two-year-old and an unknown influenza vaccination history. Both case-patients developed symptoms in mid-December and both resulted in mild neurologic sequelae. The death occurred in a six-year-old of McLeod County. The child had a history of severe static encephalopathy secondary to a motor vehicle accident. He was admitted to the hospital in early January with respiratory distress identified as influenza A pneumonia; the child had a DNR/DNI order and died in late January.

The MDH Public Health Laboratory received 919 influenza isolates for viral confirmation and strain identification. Of these isolates, 911 (99.1%) were influenza type A (H3); 1 (0.1%) was A (H1); 1 (0.1%) was B, 1 (0.1%) was B Sichuan-like, and 5 (0.5%) were A (with unidentifiable strains). Influenza type A/Fujian (H3N2) was the predominant strain circulating nationally, representing 88% of influenza A viruses typed at CDC. The predominant influenza strain, influenza A (H3), circulating in Minnesota during 2003-2004 was not well matched to the strains in the influenza vaccine used in 2003-2004. 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 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 2003-2004, MDH received reports of probable ILI outbreaks from 92 schools in 40 counties throughout Minnesota and possible outbreaks in 77 schools in 35 counties. Schools began reporting ILI outbreaks in late October; 76% of the probable and possible ILI outbreaks were reported during December. 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 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. Fortyfour long-term care facilities reported confirmed or suspected ILI outbreaks in 2003-2004. In 41 (93%) of these facilities, influenza was laboratoryconfirmed by rapid tests or culture. Thirty-four (77%) facilities reported outbreaks between mid-December and mid-January. 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.

Avian influenza surveillance efforts worldwide identified two highly pathogenic avian influenza (HPAI) strains that infected humans. In mid-December the Republic of Korea reported sudden deaths of chickens on a poultry farm; the pathogen was determined to be an HPAI (h3N1) strain. Three weeks later, a severe respiratory illness was reported in 11 previously healthy Vietnamese children who were hospitalized in Hanoi. Testing performed on two fatal cases from this cluster revealed HPAI (h3N1) as the pathogen. During this time, several poultry outbreaks of HPAI were reported in Vietnam. Japan, Indonesia, Thailand, China, Cambodia, Laos followed shortly thereafter also with reports of poultry outbreaks. Thailand and Vietnam have been the only countries to date to report human cases of avian influenza during this outbreak. The World Health Organization (WHO) has confirmed 12 h3N1 cases in Thailand with 8 deaths and 22 h3N1 cases in Vietnam with 15 deaths (68% case-fatality rate overall). Human-to-human transmission was initially suspected in a family cluster of cases in Vietnam; this has been ruled out. Reports of avian influenza outbreaks in poultry continue to be reported in Southeast Asia.

In late March, two Canadian poultry farmers were infected with the H7 avian influenza strain, both have recovered from the disease that manifested in conjunctivitis and mild respiratory symptoms. As a result of these human infections, the WHO elevated the global pandemic preparedness level from 0.1 to 0.2. Level 0.2 indicates that more than one human case caused by a new subtype of influenza has been identified in a local event. Avian influenza continues to be reported in British Columbia. In response to the avian influenza outbreaks and emergency response infrastructure changes, MDH is currently updating its influenza pandemic plan.

The events of the 2003-2004 influenza season emphasized many critical components to managing influenza. These include vaccinating at-risk patients and health care workers annually, and carefully evaluating patients with severe influenza for travel and exposure histories that could indicate a potential novel strain.

• For up to date information see>> Influenza (Flu)
• Full issue>> Annual Summary of Communicable Diseases Reported to the Minnesota Department of Health, 2003