Rubella / German Measles

2025 Case Definition

CSTE Position Statement Number: 24-ID-10

Background

Acquired rubella, also known as “German measles”, is an acute viral illness that may be characterized by low-grade fever and mild maculopapular erythematous rash; about 25–50% of rubella infections are asymptomatic. Transmission occurs primarily via droplets or direct contact with nasal secretions of infected persons. The average incubation period of rubella virus is 17 days, with a range of 12 to 23 days.1 Persons with rubella are most infectious when rash is erupting, but they can shed virus from 7 days before to 7 days after rash onset. Prodromal symptoms may include fever, conjunctivitis, and lymphadenopathy. Arthralgia or arthritis are commonly observed in adults, particularly in women, and rare complications include thrombocytopenic purpura and encephalitis. Rubella infection in pregnancy can result in serious outcomes, such as miscarriage, stillbirth, or congenital rubella syndrome (CRS), which is commonly characterized by hearing impairment, heart defects, and eye anomalies.2

Clinical Criteria

In the absence of a more likely alternative diagnosis:

Acute onset of generalized maculopapular rash, and
Fever (measured [greater than 99.0°F] or subjective), and
- Lymphadenopathy (cervical), OR
- Arthralgia or arthritis, OR
- Conjunctivitis

Laboratory Criteria

Confirmatory Laboratory Evidence:

Detection of rubella virus (e.g., RT-PCR, culture, next generation sequencing [NGS]) OR
Significant rise, defined as seroconversion or at least a 4-fold rise in titer, observed in paired acute and convalescent serum rubella IgG antibody levels*, OR
Positive serologic rubella IgM antibody*, ** AND low IgG avidity*

Presumptive Laboratory Evidence:

Positive serologic rubella IgM antibody*, **, ‡

Note: The categorical labels used here to stratify laboratory evidence are intended to support the standardization of case classifications for public health surveillance. These categorical labels should not be used to interpret the utility or validity of any laboratory test methodology.

*In the absence of rubella vaccination during the previous 6-45 days.

**Acquired rubella was suspected, testing not conducted as part of routine immunity screening (e.g., titers for employment documentation).

‡When not superseded by more specific testing in a public health laboratory.

Epidemiologic Linkage

Contact with a laboratory-confirmed^ rubella or congenital rubella case during the case’s likely infectious period, OR
Close contact (e.g., household contact) with a laboratory-confirmed^ rubella or congenital rubella case during the case’s likely infectious period, OR
International travel in the 23 days prior to rash onset, OR
Gave birth to an infant with confirmed congenital rubella^^

^“Laboratory-confirmed” case is a case that meets confirmatory laboratory evidence.

^^When residency criteria are met for pregnant woman at time of presumed illness.

Criteria to Distinguish a New Case from an Existing Case

The following should be enumerated as a new case‡‡:

Person newly meets the criteria for a confirmed or probable case,
Person who was previously reported but not enumerated as a confirmed or probable case, but due to subsequently available information now meets the criteria for a confirmed or probable case.

‡‡Note: Persistent rubella infections and congenital rubella syndrome should not be enumerated as new cases.

Case Classification

Probable

Meets clinical criteria AND meets presumptive laboratory evidence AND lacks presumptive evidence of rubella immunity prior to infection.

Confirmed

Meets confirmatory laboratory evidence, OR
Meets presumptive laboratory evidence AND epidemiologic linkage criterion of “contact with a laboratory-confirmed^ rubella or congenital rubella case during the case’s likely infectious period”, OR
Meets clinical criteria, AND
- Meets epidemiologic linkage criterion of “close contact (e.g., household contact) with a laboratory-confirmed^ rubella or congenital rubella case during the case’s likely infectious period”, OR
- Meets presumptive laboratory evidence AND meets epidemiologic linkage criterion of “international travel in the 23 days prior to rash onset” AND lacks presumptive evidence of rubella immunity prior to infection, OR
Meets epidemiologic linkage criterion of “gave birth to an infant with confirmed congenital rubella.”