Several influenza surveillance methods are employed. 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 began during the 2003-2004 influenza season, and was expanded statewide 2008-2009. Since the 2013- 2014 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 testing. In the 2014-2015 season, influenza B subtyping was added.
During the 2015-2016 season, there were 1,501 laboratory-confirmed hospitalized cases (27.5 cases per 100,000 persons compared to 77.2 cases per 100,000 in 2014-2015) reported. Cases included 1,327 influenza A (590 A[H1N1]pdm09, 41 H3, and 695 unknown A type), 156 influenza B (55 of Yamagata lineage, 3 of Victoria lineage), 6 positive for both influenza A and B, and 12 of unknown influenza types. Among the cases, 16% were 0-18 years of age, 21% were 19-49 years of age, 28% were 50-64 years of age, and 35% were ≥65 years of age. Residents of the metropolitan area made up 65% of cases.
Case report forms have been completed on 70% of 976 metropolitan area cases. Of these, 32% were diagnosed with pneumonia, 20% required admission into an intensive care unit, and 10% were placed on mechanical ventilation. An invasive bacterial co-infection was present in 9% of hospitalized cases. Antiviral treatment, recommended for all hospitalized influenza cases, was prescribed for 85% of cases. Overall, 93% of adult cases and 45% of pediatric cases had at least one chronic medical condition that would have put them at increased risk for influenza disease.
There were 3 pediatric influenza-associated deaths.
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 healthcare 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 October 4, 2015 - May 21, 2016, laboratories reported data on 21,273 influenza PCR tests, 1,617 (8%) of which were positive for influenza. Of these, 687 (43%) were positive for influenza A(H1N1)pdm09, 21 (1%) were positive for influenza A/(H3), 649 (40%) were positive for influenza A-not subtyped, and 260 (16%) were positive for influenza B.
We conduct sentinel surveillance for 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 22 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 March 6-12, 2016 at 2.4%.
Influenza Incidence Surveillance Project
MDH was one of eight nationwide sites to participate in an Influenza Incidence Surveillance Project for the 2015-2016 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 seen within five age groups, 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 13 other respiratory pathogens. Minimal demographic information and clinical data were provided with each specimen.
From July 26, 2015 – May 21, 2016, these clinics saw 1,208 ILI and 6,807 ARI patients. They submitted 724 specimens for influenza and respiratory pathogen testing, 54 (7%) of which were positive for influenza. Of those, 6 were positive for influenza A/(H3), 1 was positive for influenza A-type unspecified, 9 were positive for influenza B/Yamagata lineage, 1 was positive for influenza B-lineage unspecified, and 2 were positive for influenza C. In addition to influenza, the following pathogens were detected by PCR: 23 (3%) adenovirus, 21 (3%) human metapneumovirus, 23 (3%) RSV, 128 (18%) rhinovirus, 6 (0.8%) enterovirus, 14 (2%) parainfluenza virus 1, 2 (0.3%) parainfluenza virus 2, 6 (0.8%) parainfluenza virus 3, 7 (1%) parainfluenza virus 4, 2 (0.3%) coronavirus 229E, 7 (1%) coronavirus OC43, and 14 (2%) coronavirus NL63, and 9 (1%) coronavirus HKU1 (note: these coronaviruses are not SARS-CoV 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 primary influenza symptoms reported among students. The definition of ILI outbreaks changed 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 when the highest was 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. Forty-eight facilities in 23 counties reported confirmed outbreaks during the 2015-2016 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, 2015