Influenza Surveillance Update - Week ending November 28, 2015

This is the first influenza surveillance report for the 2015-2016 influenza season.

Marin

During the first eight weeks of the 2015-2016 influenza season (October 4-November 28, 2015), influenza activity in Marin remained minimal and within expected levels for early in the season.  We observed one outbreak in a skilled nursing facility, which contributed to the increase in positive influenza tests in week 44 (Figure 2, week starting date November 1).  

Influenza-like illness activity: 

Influenza-like illness activity in Marin County was minimal during week 47 (November 22 - 28, 2015).  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) was 8.58% during week 47.  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, 2013-2014, 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.

Influenza testing¹:  During week 47, 2 (5.9%) of the 34 specimens tested for influenza were positive.  There was one positive influenza A specimen and one positive influenza B specimen.  During this influenza season through November 28, 13 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.

California

• During week 47, the geographic distribution of influenza activity in California was sporadic^~.
• Outpatient ILI activity as a percentage of total visits to sentinel providers was 1.0% in week 47.
• Of the 1,298 specimens tested by the Respiratory Laboratory Network and Sentinel Laboratories during week 47, 15 (1.2%) were positive for influenza; of these, 4 (26.7%) were positive for influenza B and 11 (73.3%) were positive for influenza A.  Of the influenza A specimens, 5 (45.5%) were subtyped as seasonal A (H3) and 6 (54.5%) 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 4.9% during week 47.
• No specimens from California residents have been strain-typed this season.
• California Department of Public Health has received two reports of influenza-associated deaths in persons under age 65 during the 2015-2016 influenza season to date.  None of these fatalities were reported in week 47.  
• The California Department of Public Health's Influenza website contains guidance and additional data.

United States

• December 6-12, 2015 is National Influenza Vaccination Week (NIVW), which aims to promote the importance of continuing influenza vaccination.  For more information, visit the Center for Disease Control and Prevention's NIVW website.
• ​Influenza activity in the United States increased slightly, but remained low overall in week 47.
• Of the 11,288 specimens tested and reported by U.S. World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories during week 47, 171 (1.5%) were positive for influenza.
• The proportion of deaths due to pneumonia and influenza (P&I) was below the epidemic threshold.
• No influenza-associated pediatric deaths were reported during week 47.
• The proportion of outpatient visits for influenza-like illness (ILI) was 1.9% during week 47.
• Three of 10 regions reported a proportion of outpatient visits for ILI at or above the region-specific baseline level during week 47.  ILI activity was moderate in two states, low in four states, and minimal in New York City and 44 states during week 47.
• During week 47, the geographic spread of influenza activity was reported as local^ in seven states and sporadic^~ in 38 states and the District of Columbia.  Five states reported no influenza activity.  See map below.
• 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
Epidemiology Fellow
(415) 473-6020
HHannah@marincounty.org

This publication is provided to you by the Office of the Public Health Officer, County of Marin Department of Health and Human Services.

Sources

California Department of Public Health. https://www.cdph.ca.gov/HealthInfo/discond/Documents/2015%2011%2028%20Influenza%20Report.pdf. Accessed 12/07/2015.

Centers for Disease Control and Prevention. https://www.cdc.gov/flu/weekly/. Accessed 12/07/2015.