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NOTE: A surveillance case definition is a set of uniform criteria used to define a disease for public health surveillance. Surveillance case definitions enable public health officials to classify and count cases consistently across reporting jurisdictions. Surveillance case definitions are not intended to be used by healthcare providers for making a clinical diagnosis or determining how to meet an individual patient’s health needs.

CSTE Position Statement(s)

  • 09-ID-55

Case Classification


Any generalized rash illness of acute onset that does not meet the criteria for probable or confirmed rubella or any other illness


In the absence of a more likely diagnosis, an illness characterized by all of the following:

  • Acute onset of generalized maculopapular rash; AND
  • Temperature greater than 99.0°F or 37.2°C, if measured; AND
  • Arthralgia, arthritis, lymphadenopathy, or conjunctivitis; AND
  • Lack of epidemiologic linkage to a laboratory-confirmed case of rubella; AND
  • Noncontributory or no serologic or virologic testing.


  • A case with or without symptoms who has laboratory evidence of rubella infection confirmed by one or more of the following laboratory tests:
    • Isolation of rubella virus; OR
    • Detection of rubella-virus specific nucleic acid by polymerase chain reaction; OR
    • Significant rise between acute- and convalescent-phase titers in serum rubella immunoglobulin G antibody level by any standard serologic assay; OR
    • Positive serologic test for rubella immunoglobulin M (IgM) antibody;


  • An illness characterized by all of the following:
    • Acute onset of generalized maculopapular rash; AND
    • Temperature greater than 99.0°F or 37.2°C; AND
    • Arthralgia, arthritis, lymphadenopathy, or conjunctivitis; AND
    • Epidemiologic linkage to a laboratory-confirmed case of rubella.

Epidemiologic Classification

Internationally imported case: An internationally imported case is defined as a case in which rubella results from exposure to rubella virus outside the United States as evidenced by at least some of the exposure period (12–23 days before rash onset) occurring outside the United States and the onset of rash within 23 days of entering the United States and no known exposure to rubella in the U.S. during that time. All other cases are considered U.S.-acquired cases.

U.S.-acquired case: A U.S.-acquired case is defined as a case in which the patient had not been outside the United States during the 23 days before rash onset or was known to have been exposed to rubella within the United States.

U.S.-acquired cases are subclassified into four mutually exclusive groups:

  • Import-linked case: Any case in a chain of transmission that is epidemiologically linked to an internationally imported case.
  • Imported-virus case: a case for which an epidemiologic link to an internationally imported case was not identified but for which viral genetic evidence indicates an imported rubella genotype, i.e., a genotype that is not occurring within the United States in a pattern indicative of endemic transmission. An endemic genotype is the genotype of any rubella virus that occurs in an endemic chain of transmission (i.e., lasting ≥12 months). Any genotype that is found repeatedly in U.S.-acquired cases should be thoroughly investigated as a potential endemic genotype, especially if the cases are closely related in time or location.
  • Endemic case: a case for which epidemiological or virological evidence indicates an endemic chain of transmission. Endemic transmission is defined as a chain of rubella virus transmission continuous for ≥12 months within the United States.
  • Unknown source case: a case for which an epidemiological or virological link to importation or to endemic transmission within the U.S. cannot be established after a thorough investigation. These cases must be carefully assessed epidemiologically to assure that they do not represent a sustained U.S.-acquired chain of transmission or an endemic chain of transmission within the U.S.

Note: Internationally imported, import-linked, and imported-virus cases are considered collectively to be import-associated cases.

States may also choose to classify cases as "out-of-state-imported" when imported from another state in the United States. For national reporting, however, cases will be classified as either internationally imported or U.S.-acquired.


Serum rubella IgM test results that are false positives have been reported in persons with other viral infections (e.g., acute infection with Epstein-Barr virus [infectious mononucleosis], recent cytomegalovirus infection, and parvovirus infection) or in the presence of rheumatoid factor. Patients who have laboratory evidence of recent measles infection are excluded.

Related Case Definition(s)