Technical Notes

Case Ascertainment and Case Reporting

For health department staff to report cases of viral hepatitis to CDC, systems and processes must be in place that ensure each case is reported. Because of varying state laws, resources, and infrastructure, not all health departments report all cases of perinatal, acute, or chronic viral hepatitis to CDC. Additionally, diagnosing every acute case is impossible because symptoms might be either so mild that the person does not seek care or too vague to prompt a healthcare provider to suspect and test for viral hepatitis.

Case reporting begins when a local or state health department receives a positive laboratory report, indicating a person has a viral hepatitis infection. Because initial reporting provides limited information and additional laboratory test results or clinical symptoms are frequently needed for classifying cases, reported cases might require extensive follow-up to obtain full information for establishing case status and case classification.

In September 2021, CDC released the Viral Hepatitis Surveillance and Case Management: Guidance for State, Territorial, and Local Health Departments. The purpose of the document is to provide jurisdictional guidance to implement and improve hepatitis A, hepatitis B, and hepatitis C surveillance and case management, including reporting requirements, collection of relevant laboratory data, and case investigation. Given that current systems for the surveillance and follow-up of cases differ by jurisdiction, the standards are designed to provide models for best practices, recognizing that not every jurisdiction can meet those standards with available resources.

Health departments prioritize cases for follow-up using their own protocols and might submit cases to CDC with incomplete or missing information. Additionally, the volume of laboratory reports for viral hepatitis infections might be so large that not all health departments are able to consistently detect and report all acute and chronic cases to CDC. Data regarding chronic hepatitis B and hepatitis C infections are included in this report where available; however, these are newly reported chronic viral hepatitis cases and do not measure prevalence.

Information on gender identity is not available through the current data collection mechanisms to NNDSS. Gender identity is a data element for collection in the Hepatitis Message Mapping Guide, version 2.0 that is currently being piloted for implementation. Once implemented, CDC will be able to collect and publish viral hepatitis surveillance data on gender identity. The new data element will enable CDC to include statistics on both transgender people and cisgender people.

Finally, many staff in health departments were reassigned to work on the COVID-19 pandemic during 2020 and 2021, which will have affected a health department’s ability to investigate and report viral hepatitis cases in its jurisdiction.

All viral hepatitis conditions with no reported cases or characterized as Not Reportable or Data Unavailable for 2021 in a jurisdiction’s final signed report to CDC’s National Center for Surveillance, Epidemiology, and Laboratory Services (CSELS) were reported according to the following notation:

• —: No reported cases. The reporting jurisdiction did not submit any cases to CDC.
• N: Not reportable. The disease or condition was not reportable by law, statute, or regulation in the reporting jurisdiction.
• U: Unavailable. The data are unavailable.

Summary of State or Jurisdiction Reporting Exceptions for Viral Hepatitis Surveillance,* 2021

Notes:

• ^* Perinatal hepatitis B and hepatitis C are not included in this table.
• n/a: No state/jurisdiction had the reporting exception.

Urbanicity: Urban and rural categorization was made according to CDC’s 2013 National Center for Health Statistics (NCHS) urban-rural classification scheme for counties and county-equivalent entities. Large central metropolitan, large fringe metropolitan, medium metropolitan, and small metropolitan counties were grouped as urban. Micropolitan and noncore counties were grouped as rural.

US Department of Health and Human Services regions provide a standardized structure for grouping jurisdictions into larger geographic areas. Ten regional offices directly serve state and local organizations.

US Department of Health and Human Services Regions

*US territories are not included in this report, unless otherwise noted.

Case Definitions

To ensure consistent reporting across states, the Council of State and Territorial Epidemiologists (CSTE), in collaboration with CDC, developed case definitions for viral hepatitis A, hepatitis B, and hepatitis C.

The case definitions facilitate standardized reporting by using uniform criteria and differentiating between acute (A, B, and C), chronic (B and C), and perinatal cases (B and C). When new technologies are developed for laboratory testing or better clinical data become available, the case definitions are updated.

Changes in case definitions should be considered when examining temporal trends. For more information regarding the case definitions used in 2021, visit the National Notifiable Diseases Surveillance System (NNDSS) website.

New case definitions for acute and chronic hepatitis C were implemented in 2020. As outlined in the CSTE Hepatitis C Position Statement,¹ the 2020 acute hepatitis C case definition was developed to emphasize more objective laboratory tests and reduce dependence on subjective and non-specific signs and symptoms. The change minimizes variability of practice in case classification among jurisdictions and was expected to increase the number of cases classified as acute hepatitis C relative to the 2016 hepatitis C case definition, but the magnitude of the increase in acute hepatitis C cases reported will vary across jurisdiction. Variation can be due to the types of positive and negative hepatitis laboratory results and liver function tests (i.e., alanine transaminase (ALT) and total bilirubin) that are reportable by law or mandated in the jurisdiction and available to inform case classification activities, and their capacity to investigate and conduct case investigations. New case definitions for acute and chronic hepatitis B are currently under development by CSTE.

Estimating Incidence of Acute Viral Hepatitis

To account for underascertainment and underreporting, a probabilistic model for estimating the true incidence of acute hepatitis A, hepatitis B, and hepatitis C from reported cases has been published previously.² The model includes the probabilities of symptoms, referral to care and treatment, and rates of reporting to local and state health departments. The published multipliers have since been corrected by CDC to indicate that each reported case of acute hepatitis A represents 2.0 estimated infections (95% bootstrap confidence interval [CI]: 1.4–2.2); each reported case of acute hepatitis B represents 6.5 estimated infections (95% bootstrap CI: 3.7–15.9); and each reported case of acute hepatitis C represents 13.9 estimated infections (95% bootstrap CI: 11.0–47.4).

Calculation of Rates and Population Denominators

Rates per 100,000 population were calculated for the number of reported cases of hepatitis A, acute hepatitis B, chronic hepatitis B, acute hepatitis C, and chronic hepatitis C. For these five viral hepatitis conditions, US rates include the number of cases and population denominators for all states or jurisdictions that do not use the Not Reportable (N) or Unavailable (U) reporting exceptions. Denominators for rates of reported cases of viral hepatitis use population estimates from the US Census Bureau. For the years through 2020, bridged-race population estimates were used for the calculation of rates. However, the release of bridged-race population estimates ended with the release of the 2020 estimates. Beginning in 2021, single-race population estimates were used to calculate rates.

Figures and tables based on NNDSS data presented in this report use the 1977 Office of Management and Budget (OMB) standards, and race and ethnicity (Hispanic, non-Hispanic) are combined during analysis to create the following five categories: non-Hispanic American Indian/Alaska Native (AI/AN), non-Hispanic Asian/Pacific Islander (A/PI), non-Hispanic Black, non-Hispanic White, and Hispanic. These five categories will continue to be used until newer OMB standards are universally adopted for case notification to CDC. Of note, reporting of data using single-race categories may not be directly comparable with the bridged-race categories and small differences are possible.³

Mortality Surveillance, Population Denominators, and Calculation of Rates

The National Vital Statistics System (NVSS) provides information regarding deaths that occur in the United States. NVSS data in this report are from the 2017–2021 Multiple Cause of Death files in the CDC WONDER online database.^4,5 These data are based on information from all death certificates filed in the vital records offices of the 50 states and the District of Columbia through the Vital Statistics Cooperative Program. Deaths of nonresidents (e.g., nonresident aliens, nationals living abroad, or residents of US territories) and fetal deaths are excluded.

Rates per 100,000 population were calculated for the number of deaths where hepatitis A, hepatitis B, or hepatitis C were listed as a cause of death. Death rates for race and ethnicity, sex, and overall total are age-adjusted to the US standard population during 2000. For 2017, the numbers and rates of deaths were calculated using the following five bridged-race categories and population estimates: non-Hispanic AI/AN, non-Hispanic A/PI, non-Hispanic Black, non-Hispanic White, and Hispanic.

Beginning in 2018, a new race categorization that reports single-race and multiple-race categories was added to NVSS, in accordance with the 2003 revision of the standard certificate of death. For 2018–2021, the following eight categories and population estimates were used: non-Hispanic AI/AN, non-Hispanic A/PI, along with separate categories for non-Hispanic Asian and non-Hispanic Native Hawaiian or Other Pacific Islander, non-Hispanic Black, non-Hispanic White, non-Hispanic multiple race, and Hispanic. Of note, reporting of data using single-race categories may not be directly comparable with the bridged-race categories and small differences are possible.³

CDC Perinatal Hepatitis B Prevention Program Surveillance

Outcome data for infants born to a gestational parent with hepatitis B virus (HBV) infection are reported by the CDC Perinatal Hepatitis B Prevention Program. This program funds 64 jurisdictions to identify pregnant persons infected with HBV and to case-manage their infants to improve receipt of post-exposure prophylaxis, hepatitis B vaccine series completion, and post-vaccination serologic testing. Data in this report are from the reporting period for the 2020 birth cohort, followed from January 1, 2020–December 31, 2021, and only includes infants managed by the program. Infants have variable lengths of follow-up time, depending on their date of birth. More information is available at the CDC Perinatal Hepatitis B Prevention Program website.