Our study was a retrospective review of hepatitis A diagnoses and vaccinations administered by SDCPH and UCSDH. SDCPH first declared a hepatitis A outbreak on March 8, 2017, and traced the first case to November 22, 2016 (Figure 1). The outbreak control vaccination initiatives began on March 10, 2017. SDCPH declared a public health emergency on September 1, 2017, and California health officials declared a state of emergency on October 13, 2017 (Figure 1). A declining number of cases resulted in lifting of the public health emergency on January 23, 2018. SDCPH declared the outbreak over on October 18, 2018 (7) (Figure 1).

UCSDH comprises 2 geographically distinct campuses within the same healthcare system. The Hillcrest campus of UCSDH is a 386-bed hospital in the urban center of the city of San Diego and is located at the epicenter of the acute hepatitis A outbreak. The Institutional Review Board at University of California San Diego reviewed this study and deemed it to be exempt from approval as a category 4 study.

Hospital-level prevention and outbreak management focused on a similar strategy. The strategy comprised 3 components: vaccinate, sanitize, and educate.

Several articles and communications on hepatitis A were published and disseminated in UCSDH patient-oriented email newsletters to educate the general public. Nurses distributed information about hepatitis A, along with personal hygiene kits, to at-risk patients. Healthcare personnel were informed of the ongoing HAV outbreak and employee vaccination clinics through regularly scheduled UCSDH communications emails.

We defined a hepatitis A case as illness that met the clinical case definition (an acute illness with a discrete onset of any signs or symptoms consistent with acute viral hepatitis and either jaundice or elevated serum alanine aminotransferase or aspartate aminotransferase) with laboratory criteria for diagnosis (positive IgM) or an epidemiologic link to a person with laboratory-confirmed hepatitis A (10). We obtained the number of hepatitis A cases in San Diego County during November 1, 2016–October 31, 2018, from SDCPH. We obtained the number of hepatitis A cases diagnosed at UCSDH from the infection prevention/clinical epidemiology unit and Epic Icon (EpicSystems), a data-mining software used in infection surveillance. We further stratified hepatitis A cases diagnosed at UCSDH on the basis of whether patients required inpatient hospitalization. We derived length of stay using Epic Icon.

We obtained the number of hepatitis A vaccines administered in San Diego County March 1, 2017–October 31, 2018, through the vaccination initiative from SDCPH. To collect the number of vaccinations administered at UCSDH, we used Epic Slicer Dicer (EpicSystems), a self-service analytics tool within the Epic EHR. We further stratified vaccinations administered at UCSDH according to the locations in which vaccinations were delivered (inpatient hospitalization, urgent care, ambulatory clinic, ED, or occupational health) and the patients’ risk factors (homelessness, illicit drug use, alcohol abuse, hepatitis B virus infection, hepatitis C virus infection, HIV infection, cirrhosis) within the EHR-based registries. The risk factors were not mutually exclusive, and we stratified data to identify patients with >1 risk factors.

During November 1, 2016–October 31, 2018, a total of 592 confirmed or probable outbreak-associated cases of HAV infection occurred in San Diego County. Although the initial cases of hepatitis A could be traced back to November 2016, the outbreak was recognized in March 2017, and cases peaked in August 2017 (Figure 2). During the 2-year period, acute hepatitis A was diagnosed in 144 patients at UCSDH. Cases began in March 2017 and peaked in July 2017 (Figures 2, 3). Among these 144 patients, 119 (83%) were hospitalized (Figure 3). In comparison, before the outbreak period (November 1, 2012–October 31, 2016), acute hepatitis A was diagnosed in 9 patients at UCSDH, of whom 5 (56%) were hospitalized.

The mean length of stay for the 119 patients admitted to UCSDH was 6.0 days (median 3.0 days, range 1–57 days) (Figure 3). Mean length of stay for all patients admitted to UC San Diego Medical Center was 5.38 days during November 1, 2016–October 31, 2018. Starting October 2017, SDCPH contracted with a hotel for housing of infectious patients. During November 1, 2016–September 31, 2017, before the availability of housing, mean length of stay for the 102 patients hospitalized was 6.4 days (range 1–57 days) (Figure 3). In comparison, during October 1, 2017–October 31, 2018, after housing became available, 17 patients were hospitalized; mean length of stay was 3.8 days (range 1–17 days) (Figure 3).

During March 1, 2017–October 31, 2018, a total of 207,862 hepatitis A vaccines were administered in San Diego County (Table 1). Vaccination efforts in San Diego County began in March 2017, sharply increased in August 2017, and peaked in October 2017. A second peak occurred around April 2018, when the second dose, which is typically given 6–12 months after the primary vaccination, was due (Figure 2). Among the 207,862 vaccines delivered in San Diego, San Diego County administered 57,052 (27%) vaccines: 23,620 (11%) by mass vaccination events, 5,820 (3%) by foot teams, and 848 (<1%) by mobile vans (Table 1). The remaining 150,810 (73%) vaccines were administered by noncounty providers; 99,931 (48%) were administered by healthcare systems, which included EDs, outpatient clinics, inpatient hospitals, and urgent care centers. Occupational health units throughout San Diego County administered 7,831 (4%) vaccines (Table 1).

At UCSDH, 10,324 vaccines were administered during March 1, 2017–October 31, 2018; 9,288 hepatitis A vaccine (Havrix; GlaxoSmithKline, https://www.gsksource.com) doses and 1,036 recombinant hepatitis A and B vaccine (Twinrix; GlaxoSmithKline) doses were administered (Table 2; Appendix Figure). Similar to vaccination efforts in the county, vaccinations at UCSDH increased sharply in August 2017 and peaked in October 2017 and then peaked again in April 2018 (Figures 4, 5). In comparison, during March 1, 2016–February 28, 2017, before the outbreak-control vaccination initiatives, a mean (± SD) of 118.7 (± 17.5) hepatitis A vaccines (Havrix) and 55.8 (± 11.8) recombinant hepatitis A and B vaccines (Twinrix) were administered each month. Most vaccines were delivered in ambulatory care clinics (7,700 [75%]), followed by urgent care centers (1,208 [12%]) and occupational health (961 [9%]) (Table 2; Figure 4). Illicit drug use was the most common risk factor (2,477 [24%]) of patients who were vaccinated at UCSDH, followed by homelessness (1,385 [13%]) and alcohol abuse (970 [9%]) (Table 2; Figure 5). For patients experiencing homelessness, vaccinations peaked in August 2017; for patients with risk factors of illicit drug use, alcohol abuse, HIV, and cirrhosis, vaccination peaked in October 2017 (Figure 5). Vaccination rates remained unchanged throughout the vaccination initiative for patients with chronic infections from hepatitis B, hepatitis C, or both (Figure 5).

A total of 882 (85.1%) of 1,036 Twinrix doses were administered in ambulatory primary and specialty care clinics. Another 117 (11%) were provided in the urgent care setting. The Twinrix vaccination series was administered to established patients who also met criteria for hepatitis B vaccination, such as patients with HIV infection, hepatitis C infection, end-stage liver disease, or active illicit drug use, and who were expected to return to complete the series. A second peak of Twinrix administration occurred 6 months later in these same clinics. In contrast, Twinrix was administered twice at the UCSD Free Clinic, which focused on care of the uninsured community.