County of Marin Health and Human Services

Influenza Surveillance Update, Two weeks ending March 19, 2016

Marin

During weeks 10 (March 6-12) and 11 (March 13-19), influenza was still circulating in Marin County. Both influenza-like illness activity (Figure 1) and the number of positive influenza tests (Figure 2) were at levels similar to the past few weeks of this influenza season, excluding a one week decline in both measures during week 9.

Influenza-like illness activity

Influenza-like illness activity in Marin County remained elevated during weeks 10 (March 6-12) and 11 (March 13-19), and increased in comparison to week 9, however, remained similar to week 8 activity. 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 13.2% during week 10 and 13.4% week 11. 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 10, 22 (22.0%) of the 100 specimens tested for influenza were positive. Of the positive specimens from week 10, 18 (81.8%) were influenza A and 4 (18.2%) were influenza B. During week 11, 21 (20.8%) of the 101 specimens tested for influenza were positive. Of the positive specimens from week 11, 16 (76.2%) were influenza A and 5 (23.8%) were influenza B. During this influenza season through March 19, 165 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

  • Outpatient ILI activity and laboratory data indicate that influenza activity in California is still elevated, but is beginning to decrease.
  • Outpatient ILI activity as a percentage of total visits to sentinel providers was above expected levels for this time of year during weeks 10 (3.4%) and 11 (3.3%).
  • Of the specimens tested by the Respiratory Laboratory Network and Sentinel Laboratories during week 10, 25.8% (1,101 of 4,270 specimens tested) were positive for influenza. Of these, 533 (48.4%) were positive for influenza A and 568 (51.6%) were positive for influenza B. Of the influenza A specimens, 66 (12.4%) were subtyped as 2009 A (H1), 14 (2.6%) were subtyped as seasonal A (H3), and 453 (85.0%) were not subtyped.
  • Of the specimens tested by the Respiratory Laboratory Network and Sentinel Laboratories during week 11, 21.1% (885 of 4,186 specimens tested) were positive for influenza. Of these, 398 (45.0%) were positive for influenza A and 487 (55.0%) were positive for influenza B. Of the influenza A specimens, 49 (12.3%) were subtyped as 2009 A (H1), 19 (4.8%) were subtyped as seasonal A (H3), and 330 (82.9%) were not subtyped.
  • The geographic spread of influenza activity in California remained widespread+ during week 11.
  • Visit the California Department of Public Health's influenza surveillance website for more information.

United States

  • Influenza activity decreased slightly, but remained elevated nationally.
  • The proportion of outpatient visits for influenza-like illness (ILI) was 3.7% during week 10 and 3.2% during week 11, 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, 23.1% (5,968 of 25,855 specimens tested) were positive for influenza during week 10 and 20.1% (4,816 of 23,946 specimens tested) were positive for influenza during week 11.
  • During week 10, the geographic spread of influenza activity was reported as widespread+ in 40 states, regional* in 10 states, and local^ in the District of Columbia. During week 11, the geographic spread of influenza activity was reported as widespread+ in 39 states, regional* in 10 states, and local^ in one state and the District of Columbia. See map below for week 11.
  • 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%2010%20-%20FINAL%20Report.pdf and http://www.cdph.ca.gov/HealthInfo/discond/Documents/Week%2011%20-%20FINAL%20Report.pdf. Accessed 3/29/2016.

Centers for Disease Control and Prevention. https://www.cdc.gov/flu/weekly/. Accessed 3/29/2016.

Blog Category: