County of Marin Health and Human Services

Influenza Surveillance Update, Two weeks ending April 2, 2016

Marin

During weeks 12 (March 20-26) and 13 (March 27-April 2), influenza was still circulating in Marin County. However, influenza activity is decreasing, with a reduction in both influenza-like illness activity (Figure 1) and the number of positive influenza tests (Figure 2) during weeks 12 and 13.

Influenza-like illness activity

Influenza-like illness activity in Marin County decreased during weeks 12 (March 20-26) and 13 (March 27-April 2) in comparison to previous weeks of this influenza season. 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 10.1% during week 12 and 9.8% week 13. 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 12, 12 (14.5%) of the 83 specimens tested for influenza were positive. Of the positive specimens from week 12, 6 (50.0%) were influenza A and 6 (50.0%) were influenza B. During week 13, 14 (15.2%) of the 92 specimens tested for influenza were positive. Of the positive specimens from week 13, 8 (57.1%) were influenza A and 6 (42.9%) were influenza B. During this influenza season through April 2, 191 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

  • Laboratory data indicate that influenza activity in California is still elevated, but is decreasing.
  • Outpatient ILI activity as a percentage of total visits to sentinel providers was above expected levels for this time of year during weeks 12 (3.1%) and 13 (1.8%).
  • Of the specimens tested by the Respiratory Laboratory Network and Sentinel Laboratories during week 12, 16.8% (600 of 3,577 specimens tested) were positive for influenza. Of these, 267 (44.5%) were positive for influenza A and 333 (55.5%) were positive for influenza B. Of the influenza A specimens, 31 (11.6%) were subtyped as 2009 A (H1), 12 (4.5%) were subtyped as seasonal A (H3), and 224 (83.9%) were not subtyped.
  • Of the specimens tested by the Respiratory Laboratory Network and Sentinel Laboratories during week 13, 16.3% (470 of 2,884 specimens tested) were positive for influenza. Of these, 229 (48.7%) were positive for influenza A and 241 (51.3%) were positive for influenza B. Of the influenza A specimens, 37 (16.2%) were subtyped as 2009 A (H1), 23 (10.0%) were subtyped as seasonal A (H3), and 169 (73.8%) were not subtyped.
  • The geographic spread of influenza activity in California remained widespread+ during week 13.
  • 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 2.9% during week 12 and 2.4% during week 13, 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, 18.3% (4,022 of 21,959 specimens tested) were positive for influenza during week 12 and 16.2% (3,383 of 20,921 specimens tested) were positive for influenza during week 13.
  • During week 12, the geographic spread of influenza activity was reported as widespread+ in 29 states, regional* in 18 states, local^ in two states and the District of Columbia, and sporadic~ in one state. During week 13, the geographic spread of influenza activity was reported as widespread+ in 25 states, regional* in 18 states, local^ in four states and the District of Columbia, and sporadic~ in three states. See map below for week 13.
  • 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%2012%20-%20FINAL%20Report.pdf and http://www.cdph.ca.gov/HealthInfo/discond/Documents/Week%2013%20-%20FINAL%20Report.pdf. Accessed 4/12/2016.

Centers for Disease Control and Prevention. https://www.cdc.gov/flu/weekly/. Accessed 4/12/2016.

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