National Notifiable Infectious Diseases and Conditions

Disease data presented in the 2021 tables reflect impacts of the COVID-19 pandemic, such as changes in exposure-related behavior, healthcare-seeking behavior, disease reporting, and public health investigations.

• CSTE adopted the first COVID-19 national surveillance case definition on April 5, 2020, and they approved a revision to the COVID-19 national surveillance case definition, effective August 5, 2020. On June 17, 2021, a revision to the COVID-19 national surveillance case definition was approved, effective September 1, 2021.

Disease data presented in the 2020 tables reflect impacts of the COVID-19 pandemic, such as changes in exposure-related behavior, healthcare-seeking behavior, disease reporting, and public health investigations.

• Beginning in the 2020 annual tables, reported cases among non-U.S. residents are displayed in a separate row in Table 2. Based on the country of usual residence (COUR) algorithm, cases are assigned to the reporting jurisdiction submitting the case to NNDSS if the case's country of usual residence is the United States, a U.S. territory, unknown, or country is not reported; otherwise, the case is assigned to the Non-U.S. Residents' category. Country of usual residence is currently not reported by all jurisdictions or for all conditions because this data element is only available in the HL7 generic version 2 and disease-specific message mapping guides. If a jurisdiction sends data in legacy formats, they are not able to send this information. Data in Table 2 are stratified into the following four categories based upon the COUR algorithm: U.S. Residents, excluding U.S. Territories; U.S. Territories; Non-U.S. Residents; and Total.
• Beginning in the 2020 annual tables, the following footnote was added to the race (Table 6) and ethnicity (Table 7) tables:
  • Any variation of disease incidence by race or ethnicity does not reflect biological differences but reflects systemic, cultural, behavioral, and social factors including structural racism.
• Beginning in the 2020 annual tables, the following category changes were made to the race table (Table 6) to align with OMB standards: “Black” changed to “Black or African American,” and “Other Race” changed to “Other or Multi-Race” to account for individuals reported as other race or multiple races.
• Beginning in the 2020 annual tables, the footnote for “Total, all stages” was modified to include congenital syphilis, which was mistakenly omitted in the footnotes in 2018 and 2019 annual tables.
• The following reporting areas may have incomplete data, due to technical or programmatic challenges while reconciling data during the COVID-19 pandemic: California, Guam, and Minnesota. 
• The following reporting areas may have incomplete data due to updates made to their data after the 2020 reconciliation period ended and there was not sufficient time before publication of the annual tables to confirm the updated counts: Idaho, Kansas, Maryland, Vermont, and Virgin Islands.
• As a result of position statements the Council of State and Territorial Epidemiologists (CSTE) approved in 2019, case definition revisions were implemented by jurisdictions in 2020 for the following conditions: acute and chronic hepatitis C, legionellosis, pertussis, plague, and spotted fever rickettsiosis. Chronic hepatitis C data are published online by the CDC's Division of Viral Hepatitis available at https://www.cdc.gov/hepatitis/statistics/SurveillanceRpts.htm.
• Changes to the 2020 annual tables as a result of approved 2019 CSTE position statements, include the following:
  • Confirmed and probable cases of plague are combined and published in the 2020 annual tables whereas only confirmed cases were published in the 2019 tables.
  • Beginning in 2020, legionellosis cases diagnosed by PCR were classified as confirmed, whereas previously those cases were classified as suspect and did not meet the publication/print criteria.
• Changes to the 2020 annual tables as a result of approved 2020 Council of State and Territorial Epidemiologists position statements include the following:
  • CSTE adopted the first COVID-19 national surveillance case definition on April 5, 2020, and they approved a revision to the COVID-19 national surveillance case definition, effective August 5, 2020. Confirmed and probable cases are published in the 2020 annual tables.
• In 2021, the NNDSS web site moved to https://www.cdc.gov/nndss/. This change impacts where to find supporting documentation and the citation in previously published tables. Specifically, the URLs have changed for the following resources:
  • NNDSS: now https://www.cdc.gov/nndss/
    (previously https://wwwn.cdc.gov/nndss/)
  • Infectious tables - see Using and Interpreting Data: now https://www.cdc.gov/nndss/data-statistics/infectious-tables/
    (previously https://wwwn.cdc.gov/nndss/infectious-tables.html)
  • Readers' Guides: now https://www.cdc.gov/nndss/data-statistics/readers-guides/
    (previously
    • for data tables 2019-current: https://www.cdc.gov/nndss/docs/Readers-Guide-WONDER-Tables-20210421-508.pdf
    • for data tables 2016-2018: https://ndc.services.cdc.gov/wp-content/uploads/Users_guide_WONDER_tables_cleared_final.pdf
      and https://wwwn.cdc.gov/nndss/document/Users_guide_WONDER_tables_cleared_final.pdf
    • for data tables 2006-2015: https://ndc.services.cdc.gov/wp-content/uploads/guide_to_interpreting_provisional_and_finalized_nndss_data_tables.pdf
      and https://wwwn.cdc.gov/nndss/document/guide_to_interpreting_provisional_and_finalized_nndss_data_tables.pdf)
  • Technical Resource Center: now https://www.cdc.gov/nndss/trc/
    (previously https://wwwn.cdc.gov/nndss/downloads.html)
  • Surveillance Case Definitions: now https://ndc.services.cdc.gov
    (previously https://wwwn.cdc.gov/nndss/conditions/)
  • MMWR Weeks Fact Sheet: now https://ndc.services.cdc.gov/wp-content/uploads/2021/02/MMWR_Week_overview.pdf
    (previously http://wwwn.cdc.gov/nndss/document/MMWR_Week_overview.pdf)
  • MMWR Weeks Calendar: now https://ndc.services.cdc.gov/event-codes-other-surveillance-resources/
    (previously http://wwwn.cdc.gov/nndss/script/downloads.aspx)

• The 2019 annual tables exclude cases of nationally notifiable conditions and diseases among non-U.S. residents. As a result, Table 2 does not include a "Non-U.S. Resident" or "Total" row, that would have been included in the table had the data been stratified into the following four categories, based upon the "country of usual residence" (COUR) algorithm: U.S. Residents, excluding U.S. Territories; U.S. Territories; Non-US. Residents; and Total. Table 2 for the 2019 annual tables only includes the first two of these stratification categories.
• The following 24 jurisdictions may have incomplete data, due to the coronavirus disease 2019 (COVID-19) pandemic: Alaska, California, Connecticut, Delaware, District of Columbia, Florida, Idaho, Indiana, Kansas, Massachusetts, Minnesota, Missouri, Montana, Nebraska, New Hampshire, New York State (excluding New York City), New York City, North Dakota, Ohio, Oklahoma, South Carolina, Tennessee, Texas, and West Virginia. In addition, the following 2 U.S. Territories may have incomplete data due to the COVID-19 pandemic: American Samoa and the U.S. Virgin Islands.
• As a result of position statements the Council of State and Territorial Epidemiologists (CSTE) approved in 2018, case definition revisions were implemented in 2019 for the following conditions: acute hepatitis A; Candida auris, clinical; diphtheria; Salmonella Typhi infection; Salmonella Paratyphi infection; listeriosis; and yellow fever.
• Changes to the 2019 annual tables as a result of approved 2018 CSTE position statements include the following:
  • Candida auris, clinical was added as a new nationally notifiable disease.
  • Salmonella Paratyphi infection and Salmonella Typhi infection replaced Paratyphoid fever and Typhoid fever, respectively.
  • Salmonellosis (excluding S. Typhi infection and S. Paratyphi infection) replaced Salmonellosis (excluding paratyphoid fever and typhoid fever).
  • Carbapenemase-producing carbapenem-resistant Enterobacteriaceae (CP-CRE) represents a consolidation of CP-CRE species Klebsiella spp, CP-CRE E. coli, and CP-CRE Enterobacter spp.
  • Confirmed cases of diphtheria are published in the 2019 annual tables whereas confirmed, probable and unknown cases were published in the 2018 tables.
  • Beginning in 2019, confirmed and probable cases of listeriosis are being reported and displayed in the annual tables, and maternal and neonatal cases are being counted separately. Before 2019, probable cases were not reported, and cases in neonates ≤60 days of age were counted as one case in a mother-infant pair.