During week 51 (December 14-20) and week 52 (December 21-27), influenza-like illness activity began increasing in Marin (Figure 1). Compared with prior weeks this season, more influenza tests were conducted and more specimens were positive during week 52. While the percent positive has not increased from prior weeks, this should serve as a reminder to all providers that it's not too late to discuss and offer immunization to our not yet vaccinated patient population.
Influenza-like illness activity
Influenza-like illness activity in Marin County was low during week 51 (December 14-20) and moderate during week 52 (December 21-27). 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) increased to 11.2% during week 51 and 15.8% during week 52. 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, 2012-13, 2013-2014, and 2014-2015 Influenza Seasons
PROVISIONAL DATA, SUBJECT TO CHANGE. The case definition for ILI is any chief complaint field that includes the following keywords or variants of the keywords: influenza, flu, influenza-like illness, pneumonia, fever, cough, and/or sore throat.
We updated the influenza-like illness (ILI) syndrome definition by broadening the list of chief complaints. As a result, the weekly percentages of visits for ILI are higher throughout the year than was seen using the prior definition, but the same general patterns from previous seasons remain. We applied the improved definition to all seasons in the graph above.
During week 51, 3 (8.1%) of the 37 specimens tested for influenza were positive. During week 52, 6 (9.1%) of the 66 specimens tested for influenza were positive. All positive specimens during weeks 51 and 52 were influenza A. During this influenza season through December 27, 24 specimens have tested positive for influenza.
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.
- A report covering California influenza activity during weeks 51 and 52 has not yet been released.
- The California Department of Public Health's Influenza website contains guidance and additional data.
- Influenza activity in the United States continued increasing in weeks 51 and 52.
- Some circulating H3N2 strains differ from the H3N2 component of this season's influenza vaccine. The vaccine is still recommended. CDC's indications for antiviral therapy are here.
- Of the 21,858 specimens tested and reported by U.S. World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories during week 51, 6,152 (28.1%) were positive for influenza. Of the 24,001 specimens tested and reported during week 52, 7,289 (30.4%) were positive for influenza.
- The proportion of deaths due to pneumonia and influenza (P&I) was at the epidemic threshold in week 51 and below the epidemic threshold in week 52.
- Four influenza-associated pediatric deaths were reported during week 51 and six were reported during week 52.
- The proportion of outpatient visits for influenza-like illness (ILI) was 5.5% during week 51 and 5.9% during week 52.
- All 10 regions reported a proportion of outpatient visits for ILI at or above the region-specific baseline level during weeks 51 and 52. ILI activity was high in 22 states, moderate in six states, low in New York City and eight states, and minimal in 14 states during week 51. ILI activity was high in 29 states, moderate in New York City and six states, low in five states, and minimal in nine states during week 52.
- During week 51, the geographic spread of influenza activity was reported as widespread+ in 36 states, regional* in 10 states, local^ in two states, and sporadic~ in two states. During week 52, the geographic spread of influenza activity was reported as widespread+ in 43 states, regional* in six states, and sporadic~ in one state. See map below for week 52.
- 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:
Jessica Cunningham-Krahl, MPH
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. https://www.cdc.gov/flu/weekly/ and https://www.cdc.gov/flu/weekly/weeklyarchives2014-2015/week51.htm. Accessed 1/8/2015.