County of Marin Health and Human Services

Influenza Surveillance Update, Week ending December 28th


Influenza-like illness activity:  Influenza-like illness activity in Marin County from December 22-28 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 0.99% during week 52.  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 52, 23 (28.8%) of the 80 specimens tested for influenza were positive.  Of the positive tests, 22 (95.7%) were influenza A and one (4.3%) was influenza B.  During the 2013-2014 influenza season through December 28, 58 specimens have tested positive for influenza.

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.


  • California Department of Public Health released an update about severe influenza.
  • During week 52, the geographic distribution of influenza activity in California was regional^.
  • Outpatient ILI activity as a percentage of total visits to sentinel providers was 3.4% in week 52.
  • Of the 1,945 specimens tested by the Respiratory Laboratory Network (RLN) and sentinel laboratories during week 52, 442 (22.7%) were positive for influenza; of these, 23 (5.2%) were positive for influenza B and 419 (94.8%) were positive for influenza A.  Of the influenza A specimens, three (0.7%) were subtyped as seasonal A (H3), 72 (17.2%) were subtyped as 2009 A (H1), and 344 (82.1%) 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 7.7% during week 52.
  • Eleven 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 52.  During the 2013–2014 influenza season, four laboratory-confirmed influenza-associated death in a person under age 65 has been reported in California. 
  • 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 week 52.
  • Of the 6,419 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 52, 1,711 (26.7%) were positive for influenza. 
  • The proportion of deaths due to pneumonia and influenza (P&I) was 6.5% in week 52, which were below the epidemic threshold for the week.
  • Two influenza-associated pediatric deaths were reported during week 52 for deaths that occurred in week 50 and week 51.
  • The proportion of outpatient visits for influenza-like illness (ILI) was 4.3% during week 52, exceeding the national baseline of 2.0%.
  • All ten regions reported a proportion of outpatient visits for ILI at or above the region-specific baseline level during week 52.  ILI activity was high in 20 states, moderate in New York City and eight states, low in six states, and minimal in 16 states during week 52.
  • During week 52, the geographic spread of influenza activity was reported as widespread* in 25 states, regional^ in 20 states, local~ in three states, and sporadic# in two states.  See map below.
  • For additional national influenza data, visit the Center for Disease Control and Prevention's influenza surveillance website.

US Geographic Distribution of Influenza, week 52

* 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 1/6/2014.

Centers for Disease Control and Prevention. Accessed 1/7/2014.

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