County of Marin Health and Human Services

Influenza Surveillance Update, Two weeks ending December 21st


Influenza-like illness activity:  Influenza-like illness activity in Marin County from December 8-21 was low.  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) increased to 0.83% during week 50 (December 8-14, 2013) and decreased to 0.60% in week 51 (December 15-21).  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 50, six (15.0%) of the 40 specimens tested for influenza were positive.  Of the 59 specimens tested for influenza during week 51, 12 (20.3%) tested positive.  All positive tests in both weeks were influenza A viruses.  To date during the 2013-2014 influenza season, 35 specimens have tested positive for influenza.  The elevated percentages since week 49 suggest that influenza virus may be circulating locally.

Although subtyping is not routinely performed on each positive specimen in Marin, two specimens were subtyped during week 50 and eight specimens during week 51; all were 2009 H1N1.  Marin's subtyping results are consistent with current California and United States patterns of nearly all influenza A specimens with subtyping performed being 2009 H1N1.

1. Laboratory results reported by Kaiser-Novato, Kaiser-San Rafael, Marin General Hospital, Novato Community Hospital, and Solano-Napa-Yolo-Marin Public Health Lab.

Visit for influenza vaccination, testing, and treatment recommendations.


  • During week 50, the geographic distribution of influenza activity in California was local~.
  • Outpatient ILI activity as a percentage of total visits to sentinel providers was 2.5% in week 50.
  • Of the 1,249 specimens tested by the Respiratory Laboratory Network (RLN) and sentinel laboratories during week 50, 108 (8.6%) were positive for influenza; of these, seven (6.5%) were positive for influenza B and 101 (93.5%) were positive for influenza A.  Of the influenza A specimens, two (2.0%) were subtyped as seasonal A (H3), 51 (50.5%) were subtyped as 2009 A (H1), and 48 (47.5%) 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 4.8% during week 50.
  • Ten specimens from California residents have been strain-typed this season; all 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 50.  During the 2013–2014 influenza season, two laboratory-confirmed influenza-associated death in a person under age 65 has been reported in California. 
  • Data for week 51 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 continued to increase during weeks 50 and 51.
  • Of the 7,294 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 50, 1,301 (17.8%) were positive for influenza.  During week 51, 1,639 (24.1%) tests were positive for influenza of 6,813 tests conducted.
  • The proportion of deaths due to pneumonia and influenza (P&I) was 6.6% in week 50 and 6.7% in week 51, which were below the epidemic threshold for each week.
  • One influenza-associated pediatric death was reported during week 50 for a death that occurred in that week.
  • The proportion of outpatient visits for influenza-like illness (ILI) was 2.3% during week 50 and 3.0% during week 51, exceeding the national baseline of 2.0%.
  • Five regions reported a proportion of outpatient visits for ILI at or above the region-specific baseline level during week 50 and eight regions reached or exceeded their baseline level during week 51.  ILI activity was high in four states, moderate in one state, low in New York City and six states, and minimal in 37 states during week 50.  Data were insufficient in two states.  ILI activity was high in six states, moderate in eight states, low in six states, and minimal in 28 states during week 51.  Data were insufficient in New York City and two states.
  • During week 50, the geographic spread of influenza activity was reported as widespread* in four states, regional^ in 20 states, local~ in 17 states, and sporadic# in 8 states.  One state reported no influenza activity.  During week 51, the geographic spread of influenza activity was reported as widespread* in 10 states, regional^ in 23 states, local~ in 12 states, and sporadic# in four states.  One state did not report.  See map for week 51 below.
  • For additional national influenza data, visit the Center for Disease Control and Prevention's influenza surveillance website.

US Geographic Distribution of Influenza, week 51

* 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

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 12/30/2013.

Centers for Disease Control and Prevention. and Accessed 12/30/2013.

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