County of Marin Health and Human Services

Influenza Surveillance Update, February 2018


Influenza-like illness activity has increased in Marin and is currently higher than in past seasons.  Few laboratory tests were positive in November and early December, however positive tests have increased since mid-December.

Influenza-like illness activity 

Discharge data from Kaiser San Rafael, Marin General Hospital, and Novato Community Hospital emergency departments showed the percentage of visits associated with influenza-like illness (ILI) has increased to high levels in January and is above expected levels for this time of year.  

Influenza testing1 

During week 4 (January 21-27), 41 (20.3%) of the 202 specimens tested for influenza were positive.  Of the positive specimens from week 4, 27 (65.9%) were influenza A and 14 (34.1%) were influenza B. During this influenza season through January 27, 447 specimens have tested positive for influenza.  See Figure 1 below.  

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 4 (January 21-27).
  • Influenza activity is decreasing but remains elevated throughout California.
  • The overall percentage of influenza detections in clinical sentinel laboratories in Week 4 (23.3%) was lower than Week 3 (24.9%). 
  • Of the specimens tested by Clinical Sentinel Laboratories, 24.9% (1,509 of 6,468 specimens tested) were positive for influenza during week 4. Of these, 829 (54.9%) were positive for influenza A and 680 (45.1%) were positive for influenza B.  Of influenza A specimens subtyped by the Respiratory Laboratory Network, 75.9% were A (H3).   
  • Visit the California Department of Public Health’s influenza website for more information.  

United States

  • Influenza activity increased nationally during week 4 (January 21-27).
  • 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, 26.1% (15,427 of 59,200 specimens tested) were positive for influenza during week 3.  Of the positive tests, 76.4% 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 2/06/2018.

Centers for Disease Control and Prevention. Accessed 02/06/2018.

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