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2022 Communicable Diseases and Epidemiology Annual Report

This report summarizes communicable disease surveillance data reported to the Public Health – Seattle & King County (PHSKC) Communicable Disease Epidemiology and Immunization Section by healthcare providers, laboratories, and the public. It includes a table with notifiable condition data from the past ten years, as well as trends by demographic characteristics and geography. Additional information about the clinical features of each condition is available on our website.

Past communicable disease reports: 

This report does not include a summary of COVID-19 data. Please refer to our COVID-19 data and reports pages for COVID-19 specific surveillance summaries.

Information about the conditions below is available from their respective program websites:

Our nurses, epidemiologists, investigators, physicians, veterinarians and administrative staff serve as “disease detectives” working to protect King County residents from infectious diseases of public health significance. Our section:  

  • Identifies and promotes the most effective prevention measures (such as vaccination and infection control measures) 
  • Monitors the occurrence of diseases in the community and describes the affected populations 
  • Identifies health disparities to help prioritize resources to communities most in need 
  • Takes action to stop the spread of infections from contaminated food, beverages, environmental sources (e.g., animals, water), or contact with sick people 
  • Helps people who have been exposed to infectious agents minimize their risk of getting sick and/or spreading infection to others 
  • Provides information to the public, health care providers, hospitals and long-term care facilities, schools, early care and education programs (such as childcare centers), and businesses to help identify, manage, and prevent infections 
  • Connects patients to treatment 
  • Investigates and responds to emerging public health threats 

Cases of infectious disease in King County residents summarized in this report represent only a fraction of the true number of cases. Approximately 40% of the reports we investigate are not ultimately classified as confirmed, probable, or suspect cases. Typically, they aren’t confirmed because either lab testing did not support the diagnosis, the case was diagnosed as a different disease, or the clinical illness did not meet the surveillance case definition. Many patients may also not seek medical care, particularly those with mild symptoms. This may also contribute to the underestimation of confirmed or probable cases.

In 2022, King County saw a continued return to pre-pandemic levels of communicable diseases. Throughout 2022, COVID-19 restrictions continued to relax and there was a notable increase in travel. This surge in travel, in addition to other changes following the initial COVID-19 response, likely contributed to this rebound; for some conditions, cases exceeded pre-pandemic levels.  

King County investigated 4,524 confirmed, probable or suspect communicable disease reports in 2022, up 17% from the previous year. Not including COVID-19, the most common reported conditions in 2022 were:

  • Chronic hepatitis C
  • Chronic hepatitis B
  • Campylobacteriosis
  • Mpox (formerly monkeypox)
  • Salmonellosis

The distribution of these cases varied by race and ethnicity. For example, the rate of mpox was highest among American Indian or Alaska Native residents (75 cases per 100,000) and Hispanic residents (47 cases per 100,00) and lowest among Asian residents (6 cases per 100,000). The rate of enteric infections such as salmonellosis was highest among Native Hawaiian or Pacific Islander residents (15 cases per 100,00) and non-Hispanic Black residents (14 cases per 100,00) and lowest among White and Asian residents (9 cases per 100,000). Rates of chronic hepatitis C were highest among American Indian or Alaska Native residents (134 cases per 100,000) whereas rates of chronic hepatitis B were highest among Asian residents (64 cases per 100,000) and Native Hawaiian or Pacific Islander residents (53 cases per 100,000).

Rates of communicable disease reports also varied by geography. For example:

  • Rates of chronic hepatitis C were highest in South King County (58 cases per 100,000). 
  • Rates of chronic hepatitis B were highest in East King County (35 cases per 100,000) and North King County (34 cases per 100,000) and 
  • Rates of campylobacteriosis were highest North King County (38 cases per 100,000). 

The dashboard allows further exploration of regional differences on the tab labeled “Population Trends.”

Enteric bacteria typically enter the body through the mouth. People are exposed through contaminated food and water, by contact with animals or their environments, or by contact with the feces of an infected person.

Case count trends for reportable enteric conditions were increasing prior to 2020, partly due to an increased use of culture independent diagnostic tests (CIDT), that rapidly identify pathogens compared to traditional methods. Following a decrease in 2020, case counts for enteric and foodborne conditions have rebounded. In 2022 King County saw substantial increases in cases of cryptosporidiosis, cyclosporiasis, Shiga toxin-producing E. coli, shigellosis and yersiniosis relative to their respective 10-year averages.

Public Health investigated an outbreak of shigellosis that began in October 2020, and continued through 2021 into 2022. This outbreak initially impacted primarily people living unsheltered (e.g., streets, tents, encampments) in the Seattle area. In 2022, Public Health continued to see a large number of shigellosis cases among people living unsheltered, but also saw an increase in shigellosis among people who were stably housed. Two hundred twenty-two cases were reported in 2022, with 20% of cases among people experiencing homelessness. Shigellosis cases peaked in January 2022, with 47 cases reported.  

The Centers for Disease Control and Prevention (CDC) consider carbapenemase-producing organisms (CPOs) such as Enterobacterales and other carbapenem-resistant gram-negative bacteria (Pseudomonas aeruginosa and Acinetobacter baumannii) an urgent threat. They can spread in healthcare settings and contribute to carbapenem antibiotic resistance. Carbapenem antibiotics are considered a last resort antibiotic when common antibiotics no longer work. This means that carbapenem resistance makes these organisms very difficult to treat.

CPOs often live in the intestine but can spread outside the gut and cause serious infections, such as urinary tract infections, bloodstream infections, wound infections, and pneumonia. Since 2014, when Public Health began tracking CPOs, case counts have remained low. In 2022, 20 CPO cases were identified, higher than the ten-year average of 12 cases and the highest yearly case count to date.  Increasing case counts may be attributed to more reporting due to heightened awareness, active case finding through screening activities, and enhanced detection though the Antibiotic Resistance Laboratory Network resource established in 2016.

Following an initial decrease in vaccine-preventable diseases in 2020, cases have remained low in 2022 relative to pre-pandemic years. Continued public health measures to prevent COVID-19 transmission may contribute to a reduction in transmission of other respiratory pathogens. There were no reported measles cases in 2022, a decrease relative to the 10-year average of 4 cases. Reported cases of mumps have continued to decrease after a large statewide outbreak in 2016 and 2017. 

Following a mild influenza season in 2021-22, King County experienced a relatively severe flu season in 2022-23. Influenza virus activity began in October 2022, earlier than typical pre-pandemic seasons. At its peak in late November, 13% of all emergency department visits in King County had an influenza diagnosis, whereas recent pre-COVID seasons peaked around 4-6%. There were 60 influenza deaths during the 2022-23 season – higher than the 5 deaths that occurred in 2021-22 and higher than the pre-pandemic 5-year average of 49 deaths. Reduced population immunity following two mild flu seasons may have contributed to the severe flu season in 2022-23, along with the reduction of COVID-19 mitigation measures. For additional information on influenza and other respiratory viruses, visit our respiratory virus dashboard

The number of hepatitis A cases have remained at baseline level in 2022, following an outbreak from 2019 to 2021 among people experiencing homelessness. For more information on hepatitis A and this outbreak, visit our  hepatitis A dashboard.

Chronic hepatitis B and C infections continue to comprise the largest proportion of communicable diseases reported to PHSKC annually. There were roughly 750 and 1,150 newly diagnosed cases of chronic hepatitis B and C reported in 2022, respectively. In 2022, chronic hepatitis C accounted for 25% (n=1,151) of all communicable disease cases reported to King County and chronic hepatitis B accounted for 16% (n=746) of all cases.

Reports of acute hepatitis B and C infections increased between 2016 and 2019. Acute hepatitis B case counts remained elevated from 2019-2021 but decreased in 2022 to a level similar to the ten-year average. Acute hepatitis C cases remained above the ten-year average in 2022.  The COVID-19 pandemic caused major disruptions to routine public health activities, including distribution of sterile syringes and harm reduction supplies, and access to medical care, such as screening and linkage to care for hepatitis C. In 2021, King County continued to see high rates of acute hepatitis C among younger people who use drugs, with particularly high rates of infection among males and people experiencing homelessness. To address these disparities, PHSKC has partnered with local healthcare facilities, community-based organizations, and outreach providers to increase access to screening and low-barrier hepatitis C treatment options.

Our Perinatal Hepatitis B Prevention Program (PHBPP) tracks hepatitis cases in pregnant people to prevent transmission of hepatitis B to their infants by ensuring the infants receive appropriate preventive treatment. In 2022, the program ensured 96% (n=156) of pregnant people with hepatitis B were enrolled, eligible infants were tested on time, and none of these infants were infected with hepatitis B virus. More information about PHBPP.

In early May of 2022, an outbreak of mpox was confirmed in the United Kingdom. This outbreak was notable because there was evidence of substantial person-to-person transmission, whereas mpox was previously known to spread primarily through contact with infected animals. Additional cases across the world soon followed. The first mpox case in King County was reported in late May. Over the rest of the year, 497 mpox cases were reported. Most mpox cases in King County were among men who reported sexual or close intimate contact with other men. For more information about mpox cases in King County, visit our mpox dashboard.

The overall number of reports of animal bites posing a risk of rabies has been on an increasing trend since 2018. The number of reports in 2022 (193 reports) was the highest in ten years and well above the 10-year average of 123 cases.

The number of malaria cases reported in 2022 (23 cases) was the highest in ten years, and higher than the ten-year average of 15 cases. The surge in travel following relaxed COVID-19 restrictions likely contributed to the increase in malaria cases.  

In May of 2022, PHSKC learned of King County residents exposed to highly pathogenic avian influenza (HPAI). HPAI is a form of influenza primarily spread among wild bird populations that can also infect domestic poultry. Humans are rarely infected with HPAI but human cases have occurred after exposure to infected birds. Between May and June 2022, 20 HPAI exposure events occurred throughout the county and PHSKC monitored 31 residents potentially exposed to HPAI. None of the exposed individuals developed symptoms or tested positive for HPAI.

In September of 2022, an outbreak of Ebola was declared in Uganda. Ebola is a deadly virus that can be transmitted person to person through contact with infected individuals, bodily fluids, or contaminated objects. CDC began notifying local health jurisdictions of travelers coming from Uganda that may have been exposed to Ebola. Between October 2022 and January 2023, PHSKC monitored 83 King County residents for symptoms of Ebola who recently returned from travel to Uganda. None of the travelers reported any symptoms and none became a case.