County of Marin Health and Human Services

Influenza Surveillance Update, Two weeks ending November 23rd

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Influenza-like illness activity:  Influenza-like illness activity in Marin County from November 10-23 was minimal.  Discharge data from Kaiser San Rafael, Marin General Hospital, and Novato Community Hospital emergency departments and visits to the Sutter Terra Linda Urgent Care Center showed the percentage of visits associated with influenza-like illness (ILI) decreased to 0.23% during week 46 (November 10-16, 2013) and 0.17% in week 47 (November 17-23).  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 Clinic, 2011-12, 2012-2013, and 2013-2014 Influenza SeasonsMarin Influenza-like illness 2011-2013

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

Influenza testing1:  During week 46, five (26.3%) of the 19 specimens tested for influenza were positive.  All five specimens were influenza A.  Of the 37 specimens tested for influenza during week 47, two (5.4%) tested positive for influenza A and none for influenza B.  To date during the 2013-2014 influenza season, nine specimens have tested positive for influenza.  Although week 46 had a high number and percentage of positive tests, the increase was not sustained in week 47.  At this time, the week of higher activity seems to be sporadic and doesn't appear to indicate increased local influenza virus circulation. 

Visit for influenza vaccination, testing, and treatment recommendations.

1. Laboratory results reported by Kaiser-Novato, Kaiser-San Rafael, Marin General Hospital, and Novato Community Hospital.


  • During week 46, the geographic distribution of influenza activity in California was sporadic#.
  • Outpatient ILI activity as a percentage of total visits to sentinel providers was 1.2% in week 46.
  • Of the 1,032 specimens tested by the Respiratory Laboratory Network (RLN) and sentinel laboratories during week 46, 15 (1.5%) were positive for influenza A and none for influenza B.  Three specimens (20%) was subtyped as seasonal A (H3), four (27%) were subtyped as 2009 A (H1), and eight (53%) 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 4.5% during week 46.
  • Two specimens from California residents have been strain-typed this season; both matched components of the 2013-2014 influenza vaccine.
  • California Department of Public Health received no reports of influenza-associated deaths in persons under age 65 during week 46.  During the 2013–2014 influenza season, one laboratory-confirmed influenza-associated death in a person under age 65 has been reported in California. 
  • Week 47 data are not yet available.
  • The California Department of Public Health's Influenza Surveillance website contains information about their program.

United States

  • Influenza activity in the United States increased slightly during weeks 46 and 47.
  • Of the 4,457 specimens tested by U.S. World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories and reported to CDC/Influenza Division during week 46, 312 (7.0%) were positive for influenza.  During week 47, 397 (7.9%) tests were positive for influenza of 4,996 tests conducted.
  • The proportion of deaths due to pneumonia and influenza (P&I) was 5.8% in both week 46 and week 47, which is below the epidemic threshold for each week.
  • No influenza-associated pediatric deaths were reported during weeks 46 and 47.
  • The proportion of outpatient visits for influenza-like illness (ILI) was 1.5% during week 46 and 1.7% during week 47, which are below the national baseline.
  • One region reported a proportion of outpatient visits for ILI at or above the region-specific baseline level during week 46 and two regions exceeded their baseline level during week 47.  ILI activity was high in one state, moderate in two states, low in four states, and minimal in New York City and 43 states during week 46.  ILI activity was high in two states, moderate in one state, low in one state, and minimal in New York City and 45 states during week 47.  One state had insufficient data to determine ILI activity levels in week 47.
  • During week 46, the geographic spread of influenza activity was reported as regional^ in four states, local~ in nine states, and sporadic# in 34 states.  Three states reported no influenza activity.  During week 47, the geographic spread of influenza activity was reported as regional^ in six states, local~ in ten states, and sporadic# in 32 states.  Two states reported no influenza activity.  See map for week 47 below.
  • For additional national influenza data, visit the Center for Disease Control and Prevention's influenza surveillance website.

US Geographic Distribution of Influenza, week 47

^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 re-cent 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

If you have any questions or comments please contact:
Jessica Cunningham, MPH
(415) 473-7346

This publication is provided to you by the Office of the Public Health Officer, County of Marin Department of Health and Human Services.


California Department of Public Health. Accessed 12/3/2013.

Centers for Disease Control and Prevention. and Accessed 12/3/2013.

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