County of Marin Health and Human Services

Influenza Surveillance Update, Two weeks ending February 6, 2016

Marin

During weeks 4 (January 24-30) and 5 (January 31-February 6), influenza was circulating in Marin County with elevated influenza-like illness activity (Figure 1). The number of positive influenza tests increased during week 5, leading to an increase in the percent positive (Figure 2).

Influenza-like illness activity

Influenza-like illness activity in Marin County was elevated during weeks 4 (January 24-30) and 5 (January 31-February 6). 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 12.9% during week 4 and 13.0% week 5. 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 4, 7 (10.3%) of the 68 specimens tested for influenza were positive. Of the positive specimens from week 4, 5 (71.4%) were influenza A and 2 (28.6%) were influenza B. During week 5, 13 (13.5%) of the 96 specimens tested for influenza were positive. Of the positive specimens from week 5, 6 (46.2%) were influenza A and 7 (53.8%) were influenza B. During this influenza season through February 6, 60 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

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 5.
  • Outpatient ILI activity as a percentage of total visits to sentinel providers was below expected levels for this time of year during weeks 4 (2.6%) and 5 (2.3%).
  • Of the specimens tested by the Respiratory Laboratory Network and Sentinel Laboratories during week 4, 17.2% (536 of 3,120 specimens tested) were positive for influenza. Of these, 271 (50.6%) were positive for influenza A and 265 (49.4%) were positive for influenza B. Of the influenza A specimens, 11 (4.1%) were subtyped as 2009 A (H1), 5 (1.8%) were subtyped as seasonal A (H3), and 255 (94.1%) were not subtyped.
  • Of the specimens tested by the Respiratory Laboratory Network and Sentinel Laboratories during week 5, 20.6% (864 of 4,189 specimens tested) were positive for influenza. Of these, 442 (51.2%) were positive for influenza A and 422 (48.8%) were positive for influenza B. Of the influenza A specimens, 38 (8.6%) were subtyped as 2009 A (H1), 12 (2.7%) were subtyped as seasonal A (H3), and 392 (88.7%) 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 2.2% during week 4 and 2.4% during week 5, 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, 6.8% (1,085 of 15,964 specimens tested) were positive for influenza during week 4 and 9.1% (1,563 of 17,175 specimens tested) were positive for influenza during week 5.
  • During week 4, the geographic spread of influenza activity was reported as widespread+ in three states, regional* in 18 states, local^ in 16 states and the District of Columbia, and sporadic~ in 12 states. No influenza activity was reported by one state. During week 5, the geographic spread of influenza activity was reported as widespread+ in seven states, regional* in 17 states, local^ in 16 states, and sporadic~ in nine states and the District of Columbia. No influenza activity was reported by one state. See map below for week 5.
  • 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%2004%20-%20FINAL%20Report.pdf and http://www.cdph.ca.gov/HealthInfo/discond/Documents/Week%2005%20-%20FINAL%20Report.pdf. Accessed 2/16/2016.

Centers for Disease Control and Prevention. https://www.cdc.gov/flu/weekly/. Accessed 2/16/2016.

Blog Category: