During weeks 52 (December 27-January 2) and 1 (January 3-9), influenza-like illness remained low in Marin. The number of influenza tests conducted and the number of positive influenza tests have both increased in comparison to the past few weeks of the influenza season, leading to an increase in the percent positive (Figure 2).
Influenza-like illness activity
Influenza-like illness activity in Marin County was low during weeks 52 (December 27-January 2) and 1 (January 3-9). 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) remained at 10.1% during both week 52 and week 1. 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, 2013-14, 2014-2015, and 2015-2016 Influenza Seasons
PROVISIONAL DATA, SUBJECT TO CHANGE. The case definition for ILI is any chief complaint that includes the following keywords or variants of the keywords: influenza, flu, influenza-like illness, pneumonia, fever, cough, and/or sore throat.
During week 52, 4 (8.9%) of the 45 specimens tested for influenza were positive. All positive specimens from week 52 were influenza A. During week 1, 4 (6.3%) of the 63 specimens tested for influenza were positive. Of the positive specimens from week 1, 3 (75%) were influenza A and 1 (25%) was influenza B. During this influenza season through January 9, 24 specimens have tested positive for influenza. See Figure 2 below.
Figure 2. Influenza Tests in Marin County, 2015-2016 Influenza Season
1. Laboratory results reported by Kaiser-Novato, Kaiser-San Rafael, Marin General Hospital, Novato Community Hospital, and Sutter Terra Linda Urgent Care.
Visit MarinFlu.org for influenza vaccination, testing, and treatment recommendations.
- The geographic spread of influenza activity in California increased to regional*.
- Outpatient ILI activity as a percentage of total visits to sentinel providers was above expected levels for this time of year during week 52 at 3.0% and below expected levels during week 1 at 1.3%.
- Of the specimens tested by the Respiratory Laboratory Network and Sentinel Laboratories, 5.4% (106 of 1,967 specimens tested) were positive for influenza during week 52 and 10.1% (354 of 3,518 specimens tested) were positive for influenza during week 1.
- Visit the California Department of Public Health's influenza surveillance website for more information.
- Influenza activity increased slightly from previous weeks.
- The proportion of outpatient visits for influenza-like illness (ILI) was 2.8% during week 52 and 2.0% during week 1.
- 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, 1.8% (247 of 13,373 specimens tested) were positive for influenza during week 52 and 3.0% (428 of 14,269 specimens tested) were positive for influenza during week 1.
- During week 52, the geographic spread of influenza activity was reported as widespread+ in two states, regional* in six states, local^ in 13 states, and sporadic~ in 27 states. No influenza activity was reported in the District of Columbia and two states. During week 1, the geographic spread of influenza activity was reported as regional* in nine states, local^ in 11 states, and sporadic~ in 28 states. No influenza activity was reported in the District of Columbia and two states. See map below for week 1.
- 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.
*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 http://www.google.org/flutrends/
If you have any questions or comments please contact:
Haylea Hannah, MSPH
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. http://www.cdph.ca.gov/HealthInfo/discond/Documents/Week%2052%20-%20FINAL%20Report.pdf and http://www.cdph.ca.gov/HealthInfo/discond/Documents/Week%2001%20-%20FINAL%20Report.pdf. Accessed 1/19/2016.
Centers for Disease Control and Prevention. https://www.cdc.gov/flu/weekly/. Accessed 1/19/2016.