Influenza, 2016

Several influenza surveillance methods are employed. 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 influenza cases in the metropolitan area was established during the 2003- 2004 influenza season and expanded statewide for the 2008-2009 season. Since the 2013-2014 season, clinicians are encouraged to collect a throat or nasopharyngeal swab, or other specimen from patients of all ages admitted to a hospital with suspect influenza, and submit the specimen to the PHL for influenza testing. For the 2014-2015 season, influenza B subtyping was added by the PHL.

During the 2016-2017 influenza season (October 1, 2016 – April 30, 2017), 3,892 laboratory-confirmed hospitalized cases (70.9 cases per 100,000 persons compared to 27.5 cases per 100,000 in 2015-2016) were reported. Of those 2,253 (58%) were from the metropolitan area. Cases included 2,631 influenza A (23 A[H1N1] pdm09, 1,152 H3, and 1,456 unknown A type), 1,232 influenza B (600 of Yamagata lineage and 36 of Victoria lineage), 5 positive for both influenza A and B, and 24 of unknown influenza types. Among the cases, 8% were <18, 10% were 19-49, 17% were 50-64, and 65% were >65 years of age. Median age was 73 years. Residents of the metropolitan area made up 58% of cases.

Pediatric Deaths

There were 2 pediatric influenza-associated deaths (both were H3).

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 laboratories perform viral culture testing (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 2, 2016 - May 20, 2017, laboratories reported data on 31,546 influenza PCR tests, 4,176 (13%) of which were positive for influenza. Of these, 312 (7%) were positive for influenza A/(H3), 33 (<1%) were positive for influenza A(H1N1) pdm09, 2,043 (49%) were positive for influenza A-not subtyped, and 1,788 (43%) were positive for influenza B.

Sentinel Surveillance

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 February 19-25 at 5.7%.

Influenza Incidence Surveillance

MDH was one of eight nationwide sites to participate in an Influenza Incidence Surveillance Project for the 2016-2017 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 13 other respiratory pathogens. Minimal demographic information and clinical data were provided with each specimen.

From July 24 2016 – June 20, 2017, these clinics saw 1,700 ILI and 6,891 ARI patients. They submitted 785 specimens for influenza and respiratory pathogen testing; 216 (28%) were positive for influenza. Of those, 150 (69%) were positive for influenza A/ (H3), 1 (<1%) was positive for influenza A(H1N1)pdm09, 3 (1%)were positive for influenza A-type unspecified, 44 (20%) were positive for influenza B/ Yamagata lineage, and 17 (8%) were positive for influenza B/Victoria lineage. In addition to influenza A and B, the following pathogens were detected by PCR: 1 (<1%) was positive for influenza C, 15 (2%) adenovirus, 16 (2%) human metapneumovirus, 27 (3%) respiratory syncytial virus, 105 (13%) rhinovirus, 3 (<1%) enterovirus, 6 (1%) parainfluenza virus 2, 10 (1%) parainfluenza virus 3, 28 (4%) coronavirus 229E, 10 (1%) coronavirus OC43, 3 (<1%) coronavirus NL63, and 17 (2%) coronavirus HKU1 (note: these coronaviruses are not SARS-virus or MERS-CoV).

ILI Outbreaks (Schools and Long Term Care Facilities)

Since 2009, schools reported outbreaks 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. Three hundred ninety-one schools in 66 counties reported ILI outbreaks during the 2016-2017 school year. The number of schools reporting ILI outbreaks since the 2009-2010 school year ranged from a low of 92 in 2013- 2014 to a high of 1,302 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 eighty-two facilities in 61 counties reported confirmed outbreaks during the 2016-2017 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, 2016