Influenza, 2013

Several surveillance methods are employed for influenza. Surveillance data are summarized by influenza season (generally October-April) rather than calendar year.

Hospitalized Cases

Surveillance for pediatric (<18 years of age), laboratory-confirmed hospitalized cases of influenza in the metropolitan area was established during the 2003-2004 influenza season. During the 2006-2007 season, surveillance was expanded to include adults. For the 2008-2009 season, surveillance was expanded statewide, although the collection of clinical information on hospitalized cases was limited to metropolitan area residents only. During the 2013-2014 season (September 29, 2013 – May 3, 2014), clinicians were encouraged to collect a throat or nasopharyngeal swab, or other specimen from all patients admitted to a hospital with suspect influenza, and submit the specimen to the PHL for influenza testing.

During the 2013-2014 influenza season, 1,540 laboratory-confirmed hospitalizations (28.6 hospitalizations per 100,000 persons compared to 57.7 per 100,000 during the 2012-2013 influenza season) were reported. Since September 29, 2013, hospitalized cases included 1,346 that were influenza A (26 H3, 650 A[H1N1]pdm09, and 670 unknown A type), 179 that were influenza B, 12 that were positive for both influenza A and B, and 3 were unknown influenza types. Among hospitalized cases, 18% were 0-18 years of age, 23% were 19-49 years of age, 29% were 50-64 years of age and 30% were 65 years of age and older. Median age was 54.6 years. Fifty-four percent of cases were residents of the metropolitan area.

Case report forms have been completed on 784 (96.9%) of 809 metropolitan area cases to date. Of these, 29% were diagnosed with pneumonia, 20% required admission into an intensive care unit, and 9% were placed on mechanical ventilation. Three percent of hospitalized influenza cases had an invasive bacterial co-infection. Eighty-five percent of cases received antiviral treatment. Overall, 90% of adult cases and 59% of pediatric cases had at least one chronic medical condition that would have put them at increased risk for influenza disease.

Deaths

For the 2013-2014 influenza season, there were no pediatric influenza-associated deaths.

Laboratory Data

The Minnesota Laboratory System (MLS) Laboratory Influenza Surveillance Program is made up of more than 110 clinic- and hospital- based laboratories, voluntarily submitting testing data on a weekly basis. These laboratories perform rapid testing for influenza and respiratory syncytial virus (RSV). Significantly fewer labs perform viral culture testing (six labs) for influenza, RSV, and other respiratory viruses. Nine laboratories perform PCR testing for influenza and three also perform PCR testing for other respiratory viruses. The PHL also provides further characterization of submitted influenza isolates to determine the hemagglutinin serotype to indicate vaccine coverage. Tracking laboratory results assists health care providers with patient diagnosis of influenza-like illness (ILI) and provides an indicator of the progression of the influenza season as well as prevalence of disease in the community. Between September 29, 2013 - May 10, 2014, virology laboratories reported 71 viral cultures positive for influenza. Of these, 66 (93%) were positive for influenza A, and 5 (7%) were positive for influenza B. The number of positive influenza cultures peaked during the week of December 29, 2013 - January 4, 2014 at 14. Between September 29, 2013 - May 10, 2014, laboratories reported data on 19,806 influenza PCR tests, 2,353 (12%) of which were positive for influenza. Of these, 1,395 (59%) were positive for influenza A(H1N1)pdm09, 34 (1%) were positive for influenza A/(H3), 783 (33%) were positive for influenza A-not subtyped, and 141 (6%) were positive for influenza B. One hundred sixty-one influenza isolates were further characterized in the PHL; 115 (71%) were characterized as influenza A(H1N1)pdm09, 4 (2%) were characterized as influenza A/(H3), 4 (2%) were characterized as influenza A-type unspecified, and 38 (24%) were characterized as influenza B/Yamagata lineage.

Influenza Sentinel Surveillance

We conduct sentinel surveillance for influenza-like illness (ILI fever ≥100° F and cough and/or sore throat in the absence of known cause other than influenza) through outpatient medical providers including those in private practice, public health clinics, urgent care centers, emergency rooms, and university student health centers. There are 26 sites in 21 counties. Participating providers report the total number of patient visits each week and number of patient visits for ILI by age group (0-4 years, 5-24 years, 25-64 years, >65 years). Percentage of ILI peaked during the week of December 22-28, 2013 at 3.5%.

Influenza Incidence Surveillance Project

MDH was one of six nationwide sites to participate in an influenza Incidence Surveillance Project for the 2013-2014 influenza season. Five clinic sites reported the number of ILI patients and acute respiratory illness (ARI; recent onset of at least two of the following: rhinorrhea, sore throat, cough, or fever) patients divided by the total patients seen by the following age groups: <1 year, 1-4 years, 5-17 years, 18-24 years, 25-64 years, and ≥65 years, each week. Clinical specimens were collected on the first 10 patients with ILI and the first 10 patients with ARI for PCR testing at the PHL for influenza and 12 other respiratory pathogens. Minimal demographic information and clinical data were provided with each specimen.

From July 28, 2013 – May 10, 2014, these clinics saw 1,852 ILI and 8,813 ARI patients. They submitted 625 specimens for influenza and respiratory pathogen testing, 62 (10%) of which were positive for influenza. Of those, 52 (84%) were positive for influenza A(H1N1)pdm09, 7 (11%) were positive for influenza A/(H3), 2 (1%) were positive for influenza A-type unspecified, and 1 (1%) was positive for influenza B. In addition to influenza, the following pathogens were detected by PCR: 20 (3%) adenovirus, 8 (1%) human metapneumovirus, 23 (4%) RSV, 83 (13%) rhinovirus, 11 (2%) parainfluenza virus 1, 12 (2%) parainfluenza virus 2, 3 (1%) parainfluenza virus 3, 7 (1%) parainfluenza virus 4, 9 (1%) coronavirus 229E, 4 (1%) coronavirus OC43, 11 (2%) coronavirus HKU1, and 6 (1%) coronavirus NL63 (note: these coronaviruses are not SARS-virus or MERS-CoV).

ILI Outbreaks (Schools and Long Term Care Facilities)

Between 1988 and 2009, a probable ILI outbreak in a school was defined as a doubled absence rate with all of the following primary influenza symptoms reported among students: rapid onset, fever, 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 was 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. Prior to the 2009-2010 influenza season, the number of schools reporting probable influenza outbreaks ranged from a low of 38 schools in 20 counties in 19961997 to 441 schools in 71 counties in 1991-1992.

The definition of ILI outbreaks changed beginning with the 2009-2010 school year. Schools reported when the number of students absent with ILI reached 5% of total enrollment, or when three or more students with ILI are absent from the same elementary classroom. Ninety-two schools in 35 counties reported ILI outbreaks during the 2013-2014 school year. This is the lowest number of schools reporting ILI outbreaks since the 2009-2010 school year with the highest being 1,302 schools in 85 counties in 2009-2010.

An influenza outbreak is suspected in a long-term care facility (LTCF) when two or more residents in a facility develop symptoms consistent with influenza during a 48- to 72-hour period. An influenza outbreak is confirmed when at least one resident has a positive culture, PCR, or rapid antigen test for influenza and there are other cases of respiratory illness in the same unit. Twenty-seven facilities in 17 counties reported confirmed outbreaks during the 2012-2013 influenza season. The number of LTCFs reporting outbreaks ranged from a low of three in 2008-2009 to a high of 209 in 2012-2013.

• For up to date information see>> Influenza (Flu)
  
• Full issue>> Annual Summary of Communicable Diseases Reported to the Minnesota Department of Health, 2013