County of Marin Health and Human Services

Influenza Surveillance Update, Two weeks ending March 5, 2016

Marin

During weeks 8 (February 21-27) and 9 (February 28-March 5), influenza was still circulating in Marin County, however, there was a marked reduction in both influenza-like illness activity and the number of positive influenza tests during week 9 (Figure 2).

Influenza-like illness activity

Influenza-like illness activity in Marin County remained elevated during weeks 8 (February 21-27) and 9 (February 28-March 5), however, decreased in comparison to recent weeks. Discharge data from Kaiser San Rafael, Marin General Hospital, and Novato Community Hospital emergency departments and visits to Sutter Terra Linda Urgent Care showed the percentage of visits associated with influenza-like illness (ILI) was 13.6% during week 8 and 12.3% week 9. See Figure 1 below.

Figure 1: Proportion of Visits due to Influenza-Like Illness (ILI): Kaiser San Rafael, MGH, and NCH Emergency Departments and Sutter Terra Linda Urgent Care, 2013-14, 2014-2015, and 2015-2016 Influenza SeasonsInfluenza-like illness, Marin County, 2012-2015

PROVISIONAL DATA, SUBJECT TO CHANGE. The case definition for ILI is any chief complaint that includes the following keywords or variants of the keywords: influenza, flu, influenza-like illness, pneumonia, fever, cough, and/or sore throat.

Influenza testing1

During week 8, 20 (23.0%) of the 87 specimens tested for influenza were positive. Of the positive specimens from week 8, 10 (50.0%) were influenza A and 10 (50.0%) were influenza B. During week 9, 11 (12.8%) of the 86 specimens tested for influenza were positive. Of the positive specimens from week 9, 7 (63.6%) were influenza A and 4 (36.4%) were influenza B. During this influenza season through March 5, 122 specimens have tested positive for influenza. See Figure 2 below.

Figure 2. Influenza Tests in Marin County, 2015-2016 Influenza Season

PROVISIONAL DATA, SUBJECT TO CHANGE.

1 Laboratory results reported by Kaiser-Novato, Kaiser-San Rafael, Marin General Hospital, Novato Community Hospital, and Sutter Terra Linda Urgent Care.

Visit MarinFlu.org for influenza vaccination, testing, and treatment recommendations.

California

  • The geographic spread of influenza activity in California remained widespread+ during week 9.
  • Outpatient ILI activity as a percentage of total visits to sentinel providers was above expected levels for this time of year during weeks 8 (3.8%) and 9 (3.8%).
  • Of the specimens tested by the Respiratory Laboratory Network and Sentinel Laboratories during week 8, 29.4% (1,602 of 5,453 specimens tested) were positive for influenza. Of these, 730 (45.6%) were positive for influenza A and 872 (54.4%) were positive for influenza B. Of the influenza A specimens, 89 (12.2%) were subtyped as 2009 A (H1), 26 (3.6%) were subtyped as seasonal A (H3), and 615 (84.2%) were not subtyped.
  • Of the specimens tested by the Respiratory Laboratory Network and Sentinel Laboratories during week 9, 29.3% (1,343 of 4,581 specimens tested) were positive for influenza. Of these, 635 (47.3%) were positive for influenza A and 708 (52.7%) were positive for influenza B. Of the influenza A specimens, 52 (8.2%) were subtyped as 2009 A (H1), 17 (2.7%) were subtyped as seasonal A (H3), and 566 (89.1%) were not subtyped.
  • Visit the California Department of Public Health's influenza surveillance website for more information.

United States

  • Influenza activity remained elevated nationally.
  • The proportion of outpatient visits for influenza-like illness (ILI) was 3.2% during week 8 and 3.5% during week 9, both above the national baseline of 2.1%.
  • Of the specimens tested and reported by the U.S. World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories, 17.6% (3,803 of 21,615 specimens tested) were positive for influenza during week 8 and 20.6% (4,918 of 23,910 specimens tested) were positive for influenza during week 9.
  • During week 8, the geographic spread of influenza activity was reported as widespread+ in 33 states, regional* in 14 states, local^ in one state and the District of Columbia, and sporadic~ in two states. During week 9, the geographic spread of influenza activity was reported as widespread+ in 37 states, regional* in 13 states, and local^ in the District of Columbia. See map below for week 9.
  • For additional national influenza data, visit the Center for Disease Control and Prevention's influenza surveillance website.

usmap07.jpg

+Widespread: Outbreaks of influenza or increases in ILI cases and recent laboratory-confirmed influenza in at least half the regions of the state with recent laboratory evidence of influenza in the state.
*Regional: Outbreaks of influenza or increases in ILI and recent laboratory confirmed influenza in at least two but less than half the regions of the state with recent laboratory evidence of influenza in those regions
^Local: Outbreaks of influenza or increases in ILI cases and recent laboratory-confirmed influenza in a single region of the state.
~Sporadic: Small numbers of laboratory-confirmed influenza cases or a single laboratory-confirmed influenza outbreak has been reported, but there is no increase in cases of ILI.

Additional flu trends can be seen in Google Flu Trends which uses aggregated Google search data in a model created in collaboration with CDC to estimate influenza activity in the United States. For more information and activity estimates from California, the U.S. and worldwide, see http://www.google.org/flutrends/

If you have any questions or comments please contact:
Haylea Hannah, MSPH
Epidemiology Fellow
(415) 473-6020
HHannah@marincounty.org

This publication is provided to you by the Office of the Public Health Officer, County of Marin Department of Health and Human Services.

Sources

California Department of Public Health. http://www.cdph.ca.gov/HealthInfo/discond/Documents/Week%2008%20-%20FINAL%20Report.pdf and http://www.cdph.ca.gov/HealthInfo/discond/Documents/Week%2009%20-%20FINAL%20Report.pdf. Accessed 3/14/2016.

Centers for Disease Control and Prevention. https://www.cdc.gov/flu/weekly/. Accessed 3/14/2016.

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