Several surveillance methods are employed for influenza. Surveillance data are summarized by influenza season (generally October-April) rather than calendar year.
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; for the 2008-2009 season surveillance was expanded statewide. Since the 2009-2010 season, clinicians are 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. For the 2014-2015 season (September 28, 2014 – May 2, 2015), influenza B subtyping was added by the PHL.
During the 2014-2015 influenza season, there were 4,211 laboratory-confirmed hospitalized cases (77.2 cases per 100,000 persons compared to 28.6 per 100,000 for 2013-2014) reported. Cases included 3,540 influenza A (2,197 H3, 1 A[H1N1] pdm09, and 1,342 unknown A type), 639 influenza B (243 of Yamagata lineage and 58 of Victoria lineage), 22 positive for both influenza A and B, and 10 of unknown influenza types. Among the cases, 11% were 0-18 years of age, 9% were 19-49 years of age, 13% were 50-64 years of age and 67% were 65 years of age and older. Median age was 76 years. Residents of the metropolitan area made up 52% of cases.
Case report forms have been completed on 57% of 2,189 metropolitan area cases to date. Of these, 25% were diagnosed with pneumonia, 12% required admission into an intensive care unit, and 6% were placed on mechanical ventilation. An invasive bacterial co-infection was present in 10% of hospitalized cases. Antiviral treatment was prescribed for 40% of cases. Overall, 91% of adult cases and 38% of pediatric cases had at least one chronic medical condition that would have put them at increased risk for influenza disease.
For the 2014-2015 influenza season, there were 10 pediatric influenza-associated deaths.
The Minnesota Laboratory System Laboratory Influenza Surveillance Program consists of more than 110 clinic-and hospital-based laboratories, voluntarily submitting testing data on a weekly basis. These laboratories perform rapid testing for influenza. Six labs perform viral culture testing for influenza, and other respiratory viruses. Nine laboratories perform PCR testing for influenza. The PHL provides further characterization of submitted influenza isolates to determine the hemagglutinin serotype to compare to vaccine strains. 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. During the 2014-2015 influenza season, laboratories reported data on 27,463 influenza PCR tests, 3,777 (14%) of which were positive for influenza. Of these, 10 (0.3%) were positive for influenza A(H1N1)pdm09, 538 (14%) were positive for influenza A/(H3), 2,406 (64%) were positive for influenza A-not subtyped, and 823 (22%) were positive for influenza B.
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 24 sites in 19 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 21-27, 2013 at 7.9%.
Influenza Incidence Surveillance Project
MDH was one of eight nationwide sites to participate in an Influenza Incidence Surveillance Project for the 2014-2015 influenza season. Four 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 and clinical data were provided with each specimen.
From July 27, 2014 – May 19, 2015, these clinics saw 3,094 ILI and 13,250 ARI patients. Of 715 specimens submitted for influenza and respiratory pathogen testing, 101 (14%) were positive for influenza. Of those, 60 (60%) were positive for influenza A/ (H3), 4 (4%) were positive for influenza A-type unspecified, 26 (26%) were positive for influenza B/Yamagata lineage, 7 (7%) were positive for influenza B/Victoria lineage, 2 (2%) were positive for influenza B-lineage unspecified, and 7 (7%) were positive for influenza C. In addition, the following pathogens were detected by PCR: 13 (2%) adenovirus, 14 (2%) human metapneumovirus, 14 (2%) RSV, 119 (17%) rhinovirus, 21 (3%) enterovirus, 7 (1%) parainfluenza virus 2, 6 (1%) parainfluenza virus 3, 2 (0.3%) parainfluenza virus 4, 3 (0.4%) coronavirus 229E, 15 (2%) coronavirus OC43, and 9 (1%) coronavirus NL63 (note: these coronaviruses are not SARS-virus or MERS-CoV).
ILI Outbreaks (Schools and Long Term Care Facilities)
The definition of ILI outbreaks beginning with the 2009-2010 school year is 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. Seven hundred five schools in 68 counties reported ILI outbreaks during the 2014-2015 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. One hundred ninety-three facilities in 68 counties reported confirmed outbreaks during the 2014-2015 influenza season. The number of LTCFs reporting outbreaks ranged from a low of 3 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, 2014