County of Marin Health and Human Services

Influenza Surveillance Update, Two weeks ending February 21

Marin

During week 6 (February 8-14) and week 7 (February 15-21), influenza-like illness activity in Marin County remained elevated (Figure 1). Compared to weeks 4 and 5, the number of positive tests decreased during weeks 6 and 7 while the total tests conducted remained high, leading to a reduction in the percent positive (Figure 2).

Influenza-like illness activity

Influenza-like illness (ILI) in Marin County was moderate during week 6 (February 8-14) and week 7 (February 15-21). 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 ILI was 14.5% during week 6 and 15.1% during week 7. See Figure 1 below. Because of the elevated levels of ILI, emergency rooms are experiencing surges in case loads and primary care providers are encouraged to assess and treat ILI symptoms when possible.

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, 2012-13, 2013-14, and 2014-15 Influenza SeasonsInfluenza-like illness, Marin County, 2012-2015

PROVISIONAL DATA, SUBJECT TO CHANGE. The case definition for ILI is any chief complaint field that includes the following keywords or variants of the keywords: influenza, flu, influenza-like illness, pneumonia, fever, cough, and/or sore throat.

We updated the influenza-like illness (ILI) syndrome definition by broadening the list of chief complaints. As a result, the weekly percentages of visits for ILI are higher throughout the year than was seen using the prior definition, but the same general patterns from previous seasons remain. We applied the improved definition to all seasons in the graph above.

Influenza testing

During week 6, 22 (10.3%) of the 214 specimens tested for influenza were positive. During week 7, 17 (9.4%) of the 180 specimens tested for influenza were positive. The majority of specimens during week 6 and week 7 were influenza A (95.5% and 82.4%, respectively) and the remaining specimens were influenza B. As of February 21, 216 positive tests have been reported for the 2014-2015 influenza season. See Figure 2 below.

Figure 2. Influenza Tests in Marin County Reported by: Kaiser-Novato, Kaiser-San Rafael, Marin General Hospital, Novato Community Hospital, and Sutter Terra Linda Urgent Care, 2014-15 Influenza Season
Influenza Tests in Marin County, 2014-2015

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

California

  • Overall influenza activity in California was widespread+ in weeks 6 and 7.
  • Outpatient ILI activity as a percentage of total visits to sentinel providers was 3.9% in week 6 and 3.7% in week 7.
  • Of the 4,611 specimens tested by the Respiratory Laboratory Network and Sentinel Laboratories during week six, 791 (17.2%) were positive for influenza; of these, 79 (10.0%) were positive for influenza B and 712 (90.0%) were positive for influenza A. Of the influenza A specimens, 132 (18.5%) were subtyped as seasonal A (H3), none were subtyped as 2009 A (H1), and 580 (81.5 %) were not subtyped. Of the 3,736 specimens tested by the Respiratory Laboratory Network and Sentinel Laboratories during week seven, 541 (14.5%) were positive for influenza; of these, 70 (12.9%) were positive for influenza B and 471 (87.1%) were positive for influenza A. Of the influenza A specimens, 134 (28.5%) were subtyped as seasonal A (H3), none were subtyped as 2009 A (H1), and 337 (71.5%) were not subtyped.
  • Kaiser Permanente hospitalization data for northern and southern California showed that the percentage of hospitalizations for flu admissions, defined as a diagnosis of "flu," "influenza," or "pneumonia" recorded in text fields at time of admission, was 8.0% during week 6 and 7.9% during week 7.
  • California Department of Public Health has received 38 reports of influenza-associated deaths in persons under age 65 during the 2014-2015 influenza season to date.
  • The California Department of Public Health's Influenza website contains guidance and additional data.

United States

  • Influenza activity in the United States decreased, but remained elevated in week 6 and week 7.
  • Some circulating H3N2 strains differ from the H3N2 component of this season's influenza vaccine. The vaccine is still recommended. CDC released additional guidance on antiviral treatment.
  • Of the 18,370 specimens tested and reported by U.S. World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories during week six, 2,381 (13.0%) were positive for influenza. During week seven, 2,236 (12.1%) tests were positive for influenza of 18,505 tests conducted.
  • The proportion of deaths due to pneumonia and influenza (P&I) was above the epidemic threshold in weeks 6 and 7.
  • During weeks 6 and 7, six influenza-associated pediatric deaths were reported in each week.
  • The proportion of outpatient visits for influenza-like illness (ILI) was 3.2% during week 6 and 3.0% during week 7.
  • All 10 regions reported a proportion of outpatient visits for ILI at or above the region-specific baseline level during weeks 6 and 7. During week 6, ILI activity was high in 12 states, moderate in five states, low in New York City and 12 states, and minimal in 21 states. During week 7, ILI activity was high in 11 states, moderate in three states, low in 16 states, and minimal in New York City and 20 states.
  • During week 6, the geographic spread of influenza activity was reported as widespread+ in 30 states, regional* in 15 states, and local^ in five states. During week 7, the geographic spread of influenza activity was reported as widespread+ in 20 states, regional* in 25 states, and local^ in five states. See map below for week 7.
  • For additional national influenza data, visit the Center for Disease Control and Prevention's influenza surveillance website.

Geographic Distribution of Influenza in the US

+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:
Jessica Cunningham-Krahl, MPH
Epidemiologist
(415) 473-7346
JCunningham@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

Centers for Disease Control and Prevention. https://www.cdc.gov/flu/weekly/ and https://www.cdc.gov/flu/weekly/weeklyarchives2014-2015/week6.htm. Accessed 3/3/2015.

California Department of Public Health. https://www.cdph.ca.gov/data/statistics/Pages/CISPDataArchive.aspx. Accessed 3/3/2015.

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