County of Marin Health and Human Services

Influenza Surveillance Update, Two weeks ending January 23, 2016

Severe Influenza Reported Nationally

The CDC released a health advisory urging rapid antiviral treatment of high risk suspect influenza patients without waiting for testing, as H1N1 viruses, which can cause more severe illness, have been more prominent in recent weeks. For more information about the predominant influenza strains observed at the state level during weeks 2 and 3, see the California section below. Currently, no cases of severe influenza have been reported in Marin.

Marin

During weeks 2 (January 10-16) and 3 (January 17-23), the number of positive influenza tests increased (Figure 2). Influenza-like illness increased during week 2 and decreased substantially during week 3, which is consistent with patterns observed at the state level during recent weeks.

Influenza-like illness activity

Influenza-like illness activity in Marin County was elevated during week 2 (January 10-16) and low during week 3 (January 17-23). 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 11.6% during week 2 and 7.3% week 31. 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.

1All data have not been received for week 3. Data are preliminary and subject to change.

Influenza testing2

During week 2, 10 (15.4%) of the 65 specimens tested for influenza were positive. Of the positive specimens from week 2, 9 (90%) were influenza A and 1 (10%) was influenza B. During week 3, 6 (9.8%) of the 61 specimens tested for influenza were positive. Of the positive specimens from week 3, 3 (50%) were influenza A and 3 (50%) were influenza B. During this influenza season through January 23, 40 specimens have tested positive for influenza. See Figure 2 below.

Figure 2. Influenza Tests in Marin County, 2015-2016 Influenza Season
Influenza Tests in Marin County, 2014-2015

2 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 increased to widespread+ during week 3.
  • Outpatient ILI activity as a percentage of total visits to sentinel providers was below expected levels for this time of year during weeks 2 (1.5%) and 3 (1.6%).
  • Of the specimens tested by the Respiratory Laboratory Network and Sentinel Laboratories, 8.4% (414 of 4,952 specimens tested) were positive for influenza during week 2. Of these, 232 (56.0%) were positive for influenza A and 182 (44.0%) were positive for influenza B. Of the influenza A specimens, 14 (6.0%) were subtyped as 2009 A (H1), 14 (6.0%) were subtyped as seasonal A (H3), and 204 (87.9%) were not subtyped.
  • Of the specimens tested by the Respiratory Laboratory Network and Sentinel Laboratories, 15.1% (453 of 2,992 specimens tested) were positive for influenza during week 3. Of these, 239 (52.8%) were positive for influenza A and 214 (47.2%) were positive for influenza B. Of the influenza A specimens, 25 (10.5%) were subtyped as 2009 A (H1), 14 (5.9%) were subtyped as seasonal A (H3), and 200 (83.6%) were not subtyped.
  • Visit the California Department of Public Health's influenza surveillance website for more information.

United States

  • Influenza activity increased slightly from previous weeks.
  • The proportion of outpatient visits for influenza-like illness (ILI) was 2.1% during week 2 and 2.2% during week 3.
  • 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, 4.2% (565 of 13,598 specimens tested) were positive for influenza during week 2 and 5.0% (680 of 13,517 specimens tested) were positive for influenza during week 3.
  • During week 2, the geographic spread of influenza activity was reported as widespread+ in three states, regional* in ten states, local^ in 12 states, and sporadic~ in 24 states. No influenza activity was reported in the District of Columbia and one state. During week 3, the geographic spread of influenza activity was reported as widespread+ in four states, regional* in 14 states, local^ in 12 states, and sporadic~ in 20 states and the District of Columbia. See map below for week 3.
  • For additional national influenza data, visit the Center for Disease Control and Prevention's influenza surveillance website.

usmap03.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%2002%20-%20FINAL%20Report.pdf and http://www.cdph.ca.gov/HealthInfo/discond/Documents/Influenza%20Weekly%20Report%20Week%20201603.pdf. Accessed 2/1/2016.

Centers for Disease Control and Prevention. https://www.cdc.gov/flu/weekly/. Accessed 2/1/2016.

Centers for Disease Control and Prevention. https://emergency.cdc.gov/han/han00387.asp. Accessed 2/3/2016.

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