County of Marin Health and Human Services

Influenza Surveillance Update, December 2017


As expected each season, influenza-like illness activity has started to increase in Marin but remains moderate.  Few laboratory tests were positive in November and early December, however preliminary laboratory data show that positive tests have started increasing since mid-December.

Influenza-like illness activity 

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 influenza-like illness (ILI) has increased to moderate levels in December but remains within expected bounds. 

Influenza testing1 

During week 50 (December 10-16), 14 (11.6%) of the 121 specimens tested for influenza were positive.  Of the positive specimens from week 50, 11 (79%) were influenza A and 3 (21%) were influenza B. During this influenza season through December 16, 64 specimens have tested positive for influenza.  See Figure 1 below.  Preliminary data for week 51 (December 17-23) show a substantial increase in positive lab tests.

Figure 1.  Influenza Tests in Marin County, 2017-2018 Influenza Season
Influenza Tests in Marin County, 2017-2018

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

Visit for influenza vaccination, testing, and treatment recommendations.


  • The geographic spread of influenza activity in California was widespreadduring week 51 (December 17-23).
  • Outpatient influenza-like illness and hospitalizations were above expected levels.
  • Of the specimens tested by Clinical Sentinel Laboratories, 34.9% (1,824 of 5,220 specimens tested) were positive for influenza during week 51. Of these, 1,469 (80.5%) were positive for influenza A and 355 (19.5%) were positive for influenza B.  Of influenza A specimens subtyped by the Respiratory Laboratory Network, 94.9% were A (H3).   
  • Visit the California Department of Public Health’s influenza website for more information.  

United States

  • Influenza activity increased nationally during week 51 (December 17-23).
  • Of the specimens tested and reported by the U.S. World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories, 22.4% (6,373 of 28,394 specimens tested) were positive for influenza during week 51.  Of the positive tests, 86.7% were influenza A.  
  • For additional national influenza data, visit the Center for Disease Control and Prevention's influenza surveillance website.

+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.

If you have any questions or comments please contact:
Lisa Santora, MD
Deputy Public Health Officer
(415) 473-4163

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 12/29/2017.

Centers for Disease Control and Prevention. Accessed 12/29/2017.

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