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Influenza Update—Week 52

Jan. 8, 2019

Data are preliminary.

Pierce County

Pierce County influenza activity continues to increase.

We received 41 reports of influenza-associated hospitalizations since week 38 (week ending Sept. 22, 2018). Hospitalized patients’ median age is 55 years; ranging from 10 months to 86 years. Hospitalized patients’ median body mass index (BMI) is 30.2 kg/m2. The third Pierce County influenza-associated death occurred week 52 (week ending Dec. 29, 2018). The deceased was over 70 years of age and had a long-term illness.

A low percentage of emergency department (ED), urgent care, and primary care visits are for influenza-like illness (ILI).

Laboratories report the proportion of specimens positive for influenza increased weeks 50 through 52.

Pierce County Influenza Hospitalizations by Season graph. For more information, call (253) 798-6410.

Pierce County Primary Care Visits for Influenza Like Illness By Age Group graph. For more information, call (253) 798-6410. 

Pierce County ED and Urgent Care Visits for Influenza Like Illness By Age Group graph. For more information, call (253) 798-6410. 

Pierce County Influenza Test Results graph. For more information, call (253) 798-6410. 

Washington

Washington influenza activity is increasing.

Department of Health received 9 reports of influenza-associated deaths. They have not received reports of pediatric influenza deaths. They received 10 reports of ILI outbreaks in long-term care facilities.

The Centers for Disease Control and Prevention (CDC) characterized ILI activity in Washington as minimal.

United States

United States influenza activity is increasing.

Influenza A(H1N1)pmd09 predominates in most of the United States, but influenza A(H3N2) and influenza B are also circulating. Outpatient visits for ILI are above the national baseline. The highest rate of influenza-associated hospitalization (14.5 per 100,000 population) is in children under 5 years of age. In hospitalized adults, obesity, metabolic disorder and cardiovascular disease are the most common comorbid conditions. In children, asthma and obesity are most common.

Comment

A disproportionate number of Pierce County residents hospitalized with influenza are obese (BMI >30 kg/m2). In 2016, 31.2% of Pierce County residents were obese. So far during the 2018-2019 influenza season, half of the Pierce County residents hospitalized with influenza were obese. During the 2017-2018 influenza season, 43% of Pierce County residents hospitalized with influenza were obese. Nationally, obesity is one of the most common comorbid conditions associated with influenza hospitalization.

Relatively few influenza viruses from Pierce County and Washington have been subtyped. Most subtyped viruses were influenza A(H1N1)pmd09. This reflects the national H1N1 predominance. Influenza seasons when H1N1 predominates are typically less severe than when H3N2 predominates. This may be due, in part, to people born before 1957 being previously exposed to H1N1. Their immune responses are more effective against H1N1 than H3N2. It is interesting to note that, so far this season, hospitalized patients’ median age is 55 years. During the 2016-2017 and 2018-2019 seasons when influenza A(H3N2) predominated, hospitalized patients’ median age was 65 and 66.5 years, respectively. Most influenza-associated deaths during the 2009 influenza A(H1N1) pandemic were people younger than 65 years of age.

This reinforces 2 current influenza immunization recommendations:

  • Obesity is a risk factor for influenza-associated complications and hospitalization.
  • Everyone 6 months of age and older should be immunized.

References

CDC. (2018). 2018-2019 Influenza Season Week 52 Ending Dec. 29, 2018. Retrieved Jan. 4, 2019 from www.cdc.gov/flu/weekly/index.htm.

Dawood, F. S., Iuliano, A. D., Reed, C., Maltzer, M. I., Shay, D. K., Cheng, P-Y., et al. (2012). Estimated global mortality associated with the first 12 months of 2009 pandemic influenza A H1N1 virus circulation: a modeling study. Lancet Infectious Diseases, 12(9), 687-695.

Washington Department of Health. (2018). Washington Influenza Update Week 52: Dec. 23-29, 2018. Retrieved Jan. 4, 2019 from www.doh.wa.gov/Portals/1/Documents/5100/420-100-FluUpdate.pdf.

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