Influenza Surveillance Update, Week ending January 18th

Marin

Severe influenza: Influenza deaths and ICU admissions for persons under age 65 years are reportable events.  County of Marin Department of Health and Human Services has received reports for the following severe influenza cases in Marin County residents as of 1/29/2014:

• 2 laboratory-confirmed influenza-associated deaths in persons under age 65
• No persons under age 65 with laboratory-confirmed influenza are currently in intensive care

Influenza-like illness activity:  Influenza-like illness activity in Marin County was moderate during week 3 (January 12-18).  Discharge data from Kaiser San Rafael, Marin General Hospital, and Novato Community Hospital emergency departments and visits to the Sutter Terra Linda Urgent Care Center showed the percentage of visits associated with influenza-like illness (ILI) increased to 1.22% during week 3.  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 Clinic, 2011-12, 2012-2013, and 2013-2014 Influenza Seasons

PROVISIONAL DATA, SUBJECT TO CHANGE. The case definition for ILI is any chief complaint field that includes the following text: influenza, flu, influenza-like illness, pneumonia, or fever/cough.

Influenza testing¹:  During week 3, 39 (22.2%) of the 176 specimens tested for influenza were positive.  Of the positive specimens during week 3, 38 (97.4%) were influenza A and 1 (2.6%) was influenza B.  During this influenza season through January 18, 169 specimens have tested positive for influenza.

Subtyping has been performed on 48 influenza A specimens from Marin facilities this season through January 21.  Forty-five (93.8%) were subtyped as H1N1 and three (6.3%) were subtyped as seasonal H3.

1. Laboratory results reported by Kaiser-Novato, Kaiser-San Rafael, Marin General Hospital, Novato Community Hospital, and Solano-Napa-Yolo-Marin Public Health Lab.

Visit MarinFlu.org for influenza vaccination, testing, and treatment recommendations.

California

• During week 3, the geographic distribution of influenza activity in California was widespread*.
• Outpatient ILI activity as a percentage of total visits to sentinel providers was 4.3% in week 3.
• Of the 4,576 specimens tested by the Respiratory Laboratory Network (RLN) and sentinel laboratories during week 3, 1,389 (30.4%) were positive for influenza; of these, 81 (1.8%) were positive for influenza B and 1,308 (28.6%) were positive for influenza A.  Of the influenza A specimens, 15 (1.1%) were subtyped as seasonal A (H3), 415 (31.7%) were subtyped as 2009 A (H1), and 878 (67.1%) 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 8.2% during week 3.
• Twenty-five specimens from California residents have been strain-typed this season; all matched components of the 2013-2014 influenza vaccine.
• California Department of Public Health received 50 reports of influenza-associated deaths in persons under age 65 during week 3. During the 2013–2014 influenza season through week 3, 95 laboratory-confirmed influenza-associated death in a person under age 65 has been reported in California.  Preliminary data show 51 additional laboratory-confirmed influenza-associated deaths in persons under age 65 reported after week 3.
• The California Department of Public Health's Influenza website contains guidance and additional data.

United States

• Influenza activity in the United States remained high in week 3.
• Of the 12,108 specimens tested by U.S. World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories and reported to CDC/Influenza Division during week 3, 2,793 (23.1%) were positive for influenza. 
• The proportion of deaths due to pneumonia and influenza (P&I) was 8.1% in week 3.
• Eight influenza-associated pediatric deaths were reported during week 3.
• The proportion of outpatient visits for influenza-like illness (ILI) was 3.4% during week 3.
• All ten regions reported a proportion of outpatient visits for ILI above the region-specific baseline level during week 3.  ILI activity was high in 13 states, moderate in New York City and seven states, low in 15 states, and minimal in 15 states during week 3. 
• During week 3, the geographic spread of influenza activity was reported as widespread* in 41 states, regional^ in eight states, local^~ in no states, and sporadic^# in one state.  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:
Jessica Cunningham, MPH
Epidemiologist
(415) 473-7346
JCunningham@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/Week%203%20-%20FINAL%20Report.pdf. Accessed 1/24/2014.

Centers for Disease Control and Prevention.  http://www.cdc.gov/flu/weekly/.  Accessed 1/29/2014.