County of Marin Health and Human Services

Influenza Surveillance Update, Two weeks ending April 16, 2016

Influenza Surveillance Update

Due to decreasing influenza activity in Marin County, we will be releasing our next and last influenza surveillance update report of the season in one month, during the last week of May. If you have any questions about influenza activity in the meantime, please reach out to Haylea Hannah at HHannah@marincounty.org or (415) 473-6020.

Marin

During weeks 14 (April 3-9) and 15 (April 10-16), influenza activity was decreasing in Marin County, with a reduction in both influenza-like illness activity (Figure 1) and the number of positive influenza tests (Figure 2).

Influenza-like illness activity
Influenza-like illness activity in Marin County decreased during weeks 14 (April 3-9) and 15 (April 10-16) in comparison to peak activity observed during 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 10.4% during week 14 and 8.9% week 15. 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 Seasonsiliwks1415.jpg

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
There was a marked reduction in the number of tests conducted during weeks 14 and 15, corresponding to a decrease in influenza-like illness. During week 142, 10 (17.5%) of the 57 specimens tested for influenza were positive. Of the positive specimens from week 14, 5 (50.0%) were influenza A and 5 (50.0%) were influenza B. During week 15, 9 (16.4%) of the 55 specimens tested for influenza were positive. Of the positive specimens from week 15, 4 (44.4%) were influenza A and 5 (55.6%) were influenza B. During this influenza season through April 16, 210 specimens have tested positive for influenza. See Figure 2 below.

Figure 2. Influenza Tests in Marin County, 2015-2016 Influenza Seasonlabwks1415final.jpg

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.

2 All data have not been received for week 14. Data are preliminary and subject to change.

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

California

  • Influenza activity is continuing to decrease in California, however, laboratory data indicate that influenza activity is still elevated in some regions.
  • Outpatient ILI activity as a percentage of total visits to sentinel providers was below expected levels for this time of year during weeks 14 (2.3%) and 15 (1.5%).
  • Of the specimens tested by the Respiratory Laboratory Network and Sentinel Laboratories during week 14, 13.8% (362 of 2,617 specimens tested) were positive for influenza. Of these, 194 (53.6%) were positive for influenza A and 168 (46.4%) were positive for influenza B. Of the influenza A specimens, 28 (14.4%) were subtyped as 2009 A (H1), 6 (3.1%) were subtyped as seasonal A (H3), and 160 (82.5%) were not subtyped.
  • Of the specimens tested by the Respiratory Laboratory Network and Sentinel Laboratories during week 15, 10.7% (227 of 2,113 specimens tested) were positive for influenza. Of these, 105 (46.3%) were positive for influenza A and 122 (53.7%) were positive for influenza B. Of the influenza A specimens, 16 (15.2%) were subtyped as 2009 A (H1), 6 (5.7%) were subtyped as seasonal A (H3), and 83 (79.0%) were not subtyped.
  • The geographic spread of influenza activity in California decreased to regional* during week 15.
  • Visit the California Department of Public Health's influenza surveillance website for more information.

United States

  • Influenza activity decreased nationally during week 15.
  • The proportion of outpatient visits for influenza-like illness (ILI) was 2.1% during week 14 and 2.1% during week 15, both at 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, 14.0% (2,544 of 18,188 specimens tested) were positive for influenza during week 14 and 13.4% (2,258 of 16,840 specimens tested) were positive for influenza during week 15.
  • During week 14, the geographic spread of influenza activity was reported as widespread+ in 18 states, regional* in 19 states, local^ in ten states and the District of Columbia, and sporadic~ in three states. During week 15, the geographic spread of influenza activity was reported as widespread+ in 14 states, regional* in 19 states, local^ in 13 states and the District of Columbia, and sporadic~ in four states. See map below for week 15.
  • For additional national influenza data, visit the Center for Disease Control and Prevention's influenza surveillance website.

usmap15.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%2014%20-%20FINAL%20Report.pdf and http://www.cdph.ca.gov/HealthInfo/discond/Documents/Week%2015%20-%20FINAL%20Report.pdf. Accessed 4/25/2016.

Centers for Disease Control and Prevention. https://www.cdc.gov/flu/weekly/. Accessed 4/25/2016.

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