County of Marin Health and Human Services

Influenza Surveillance Update, Two weeks ending October 12th

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This is the first Influenza Surveillance Update of the 2013-2014 influenza season.  The report will be prepared bi-weekly until influenza activity begins to increase, then the report will be prepared weekly.


Influenza-like illness activity:

  • Influenza-like illness activity in Marin County from September 29 through October 12 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 during week 40 (September 29-October 5, 2013) showed the percentage of visits associated with influenza-like illness (ILI) was 0.34%, increasing to 0.46% in week 41 (October 6-12).  See Figure 1 below.
  • With the addition of Kaiser San Rafael Emergency Department data starting in August 2013 (week 34), influenza-like illness calculations now include all EDs in Marin County.  Adding Kaiser data decreased the ILI percentages compared to the percentage for all non-Kaiser facilities.

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 Seasons

Marin County influenza-like illness graph

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:  No specimens tested positive for influenza during either week 40 or week 41.  Six specimens were tested for influenza in week 40 and ten specimens were tested in week 41.

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


  • State-level influenza data aren't yet available for weeks 40-41.
  • The California Department of Public Health's Influenza Surveillance website contains information about their program.

United States

  • During weeks 40 and 41, influenza activity was low in the United States.
  • Of the 3,489 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 40, 163 (4.7%) were positive for influenza.  During week 41, 166 (4.7%) tests were positive for influenza of 3,534 tests conducted.
  • The proportion of deaths due to pneumonia and influenza (P&I) was 5.7% in week 40 and 5.6% in week 41, which are both below the epidemic threshold for each week.
  • No influenza-associated pediatric deaths occurring during the 2013-2014 influenza season have been reported.
  • The proportion of outpatient visits for influenza-like illness (ILI) was 1.2% during week 40 and 1.1% during week 41, which are below the national baseline.
  • All regions reported a proportion of outpatient visits for ILI below the region-specific baseline level during weeks 40 and 41.  ILI activity was minimal in New York City and all 50 states during week 40.  ILI activity was low in two states and minimal in New York City and 48 states during week 41.  The District of Columbia had insufficient data to determine ILI activity levels.
  • During week 40, the geographic spread of influenza activity was reported as regional in Puerto Rico, local~ in three states, and sporadic# in Guam and 26 states.  The District of Columbia and 21 states reported no influenza activity.  During week 41, the geographic spread of influenza activity was reported as regional in Puerto Rico, local~ in three states, and sporadic# in the District of Columbia, Guam, and 22 states.  No influenza activity was reported in 22 states and 1 state did not report. See map for week 41 below.
  • For additional national influenza data, visit the Center for Disease Control and Prevention's influenza surveillance website.

US Influenza Geographic Distribution map

^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.

Centers for Disease Control and Prevention. and Accessed 10/22/13.

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