Rubella

March

• Case definition – reformatted to include new subsections and align with the new structure.
• Laboratory testing guidelines section – new section including removal of culture testing.

For an overview of all updates made to the Communicable Disease Control Manual, refer to Updates to the Communicable Disease Control Manual – Health New Zealand | Te Whatu Ora .

The incidence of rubella in New Zealand has decreased since the last national epidemic in 1995.

Rubella immunisation was introduced in 1970, and rubella has been a notifiable disease since 1996. The last large rubella outbreak in 1995–1996 mostly involved young adult males, who would not have been offered immunisation. This emphasises the need to immunise both boys and girls to reduce the risk of exposure in pregnant women, as well as to reduce illness in men.

More detailed epidemiological information is available on the New Zealand institute for Public Health and Forensic Science Limited (PHF Science) surveillance website (external link).

14–23 days, commonly 16–18 days.

Children and adults transmit the virus in their nasopharyngeal secretions by droplet spread or direct contact.

From about 1 week before to 1 week after the onset of the rash.

Confirmed: A person who has a clinically compatible illness and either laboratory definitive evidence or an epidemiologically link to a confirmed case.

Probable: A person who has a clinically compatible illness.

Under investigation: A person who has been notified to the medical officer of health, but information is not yet available to classify them further. 

Not a case: A person who has been investigated and subsequently found not to meet the case definition.

Note: Recent immunisation with the measles-mumps-rubella vaccine (MMR) may also result in detectable anti-rubella IgM or a significant increase in anti-rubella IgG. Because laboratories do not necessarily have access to this information, all results consistent with possible rubella infection should be reported to a medical officer of health. 

An illness with a generalised maculopapular rash, fever and one or more of the following.

• Arthralgia/arthritis
• Lymphadenopathy
• Conjunctivitis.

Rubella often presents atypically and is difficult to diagnose clinically with certainty. Up to 50% of rubella infections are subclinical. If accurate diagnosis is important, it must be laboratory confirmed.

An epidemiological link is established when there is contact between 2 people with a plausible mode of transmission at a time when one of them is likely to be infectious and the other has onset of illness within the incubation period.

Laboratory definitive evidence

If the case received a vaccine containing the rubella virus in the 6 weeks prior to symptom onset, laboratory confirmation requires evidence of infection with a wild type virus strain obtained through genetic characterisation (refer to laboratory testing guidelines).

If the case did not receive a vaccine containing the rubella virus in the 6 weeks prior to symptom onset, laboratory confirmation requires at least one of the following.

• Detection of rubella virus nucleic acid.

OR

• Detection of rubella-specific IgM antibody.

OR 

• IgG seroconversion or a significant rise (4-fold or greater) in antibody level for the virus between paired sera tested in parallel where the convalescent serum was collected 10 to 14 days after the acute serum.

Refer to Appendix 4: Direct laboratory notification of communicable diseases flowcharts for the direct laboratory notification process for Rubella.

Testing may be carried out for the following reasons.

• To confirm or exclude a diagnosis of rubella in a suspected case.
• To exclude vaccine strain virus in a suspected case who has recently been vaccinated.
• To determine rubella immune status in a contact (IgG serology).
• To track transmission pathways during a rubella outbreak.

Health practitioners should promptly notify the local medical officer of health of suspected cases.

The medical officer of health or other public health service clinical staff should discuss urgent cases with the on-call clinical microbiologist, so laboratory staff are aware of the urgency and can prioritise the sample for prompt processing. The clinical microbiologist is the point of contact with the laboratory.

A sample that requires urgent processing should be marked ‘Urgent Public Health’.

If rubella is suspected, the following should be obtained and included on the laboratory test request form.

• Symptoms including onset date.
• Vaccination status clearly stated to ensure proper processing and interpretation.
• Any known links to another case or outbreak.

Polymerase chain reaction (PCR) testing is the primary diagnostic tool. Laboratory confirmation requires detection of rubella virus nucleic acid.

Refer to laboratory criteria and case classifications for confirmed and probable case definitions.

Polymerase chain reaction (PCR)

PCR on a nasopharyngeal sample is the preferred test.

Rubella virus is detectable from 3 days before rash onset (rash onset is day 0) to 7 days after rash onset. The routine rubella PCR test does not distinguish between wild type and vaccine strain.

Genotyping is performed by the National Measles and Rubella Laboratory (NMRL) at Canterbury Health Laboratories on cases with a positive rubella PCR that do not have travel history and/or no contact or epidemiological link to a confirmed case but have a history of recent vaccination. For all other rubella PCR positive cases vaccine strain-specific PCR should only be requested after discussion between the medical officer of health and the clinical microbiologist.

PCR tests have the highest diagnostic sensitivity when samples are collected at first assessment of a suspected case (maximum sensitivity is within 3 days of rash onset, but reasonable sensitivity is observed up to 7 days after rash onset).

Nasopharyngeal or oropharyngeal samples have the highest yield particularly in the 7 days after rash onset. Discussion with a clinical microbiologist is advised if testing more than 7 days after rash onset.

All requests for rubella PCR, should have vaccination status included on the referral form.

Serology

Rubella serology is primarily used to assess immunity status (IgG) in contacts. It is generally not recommended for diagnosing infection because results can be unreliable—especially in previously vaccinated individuals or due to cross-reactivity with other viral infections.

Serology should only be used to investigate a suspected rubella case when PCR testing is not possible, and the test has been requested by a medical officer of health after discussion with a clinical microbiologist.

Recent vaccination can produce an IgM response, while previously vaccinated individuals who become infected may not develop an IgM response. IgM serology confirmed by the laboratory may occasionally help diagnosing late presentations. However, any positive IgM result should be discussed with a clinical microbiologist.

Rubella IgG detected without IgM within 1 to 2 days of a rash onset strongly suggests prior immunity and that the rash is more likely due to causes other than rubella. The IgG results also have limited value for public health decisions because a second sample is required 2 weeks after the initial blood serology test.

To ensure appropriate testing, the request form must include:

• the type of investigation is required:
  • immunity status (IgG only)
  • suspected infection (IgG and IgM)
• comprehensive clinical details, including the date of rash onset.

Serology testing will not distinguish between wild type and vaccine strain rubella.

Serology (Immunoglobulin G IgG) to determine immune status 

Serology is most useful for confirming immunity in individuals with uncertain vaccination history, although commercial tests do not detect all vaccine-induced immunity.

Refer to the Contact management section for guidance on when to do serology testing in contacts.

Genotyping

Genotyping is performed at the NMRL using Sanger sequencing of a variable region of the rubella genome. It is used to determine the wild type genotype and strain/lineage, which is useful for epidemiology and outbreak investigations.

Genotyping can also confirm whether a positive rubella PCR result is due to recent vaccination. 

Genotyping is performed on all cases with a positive rubella PCR result that do not have an epidemiological link to a confirmed case (e.g. new importations and sporadic cases). All samples referred for genotyping or vaccine-strain testing should have recent vaccination status included on the referral form.

Attending health practitioners or laboratories must immediately notify the local medical officer of health of suspected cases. Notification should not await confirmation.

See Appendix 5: Escalation pathways for more information

Ascertain if there is a history of vaccination, possible contacts and travel. Ensure laboratory confirmation by serology or detection of virus in clinical specimens has been attempted. Nasal, throat, urine, blood and cerebrospinal fluid specimens can yield the virus. Discuss testing with an infectious disease physician or a microbiologist.

In health care facilities, apply droplet and contact precautions until at least 7 days after onset of a rash in postnatal rubella. Non-immune pregnant women, in particular, should not have contact with an infectious case.

Exclude from any early childhood service, school, institution or work until fully recovered and for 7 days after onset of rash. Cases should avoid contact with women of childbearing age.

Nil specific.

Advise the case and their caregivers of the nature of the infection and its mode of transmission.

All people with close unprotected contact (for example, household, school, workplace, military camp) with the case during the week before onset of illness or during the subsequent period of communicability.

Check immunisation status of contacts.

Advise any pregnant contact to get in touch with her lead maternity carer (LMC) to check her rubella status.

A pregnant contact with confirmed immunity can be reassured that the likelihood of rubella infection is remote. This applies if:

• she has received at least two documented doses of a rubella-containing vaccine given at least four weeks apart and given after age 12 months, regardless of serology, OR
• a previous antibody screening test has detected a protective level of antibodies, and this has been documented.

Pregnant contacts whose immunity to rubella has not been confirmed must be investigated serologically as soon as possible in liaison with their LMC and primary health care doctor. The rash is not diagnostic and infection can occur without clinical symptoms. Discuss testing with an infectious diseases physician or a microbiologist.

The laboratory should test for rubella IgM and IgG. No pregnant woman under 20 weeks’ gestation should have rubella diagnosed on IgM alone. The laboratory should store (frozen) an aliquot of serum for later testing in tandem with a follow-up sample.

• If the sample is IgM positive, regardless of IgG, then a full assessment of the serological status is needed. Results must be interpreted in conjunction with the time lapse since exposure to determine whether or not acute infection has occurred. Consider further serum samples and/or testing in a reference laboratory.
• If the sample is negative for both IgM and IgG, then the woman is susceptible, and if she remains asymptomatic then a second blood specimen should be obtained 28 days after last exposure to the case. If, however, the woman develops clinical symptoms suggestive of rubella, a second blood specimen should be obtained as soon as possible. A third blood specimen may be necessary 7 days after the onset of symptoms.
• If IgG is detected and IgM is not detected, and the IgG is less than 15 IU/mL and there is a history of onset of rash in the previous 10 days, request further serum.

Diagnosis and management based on any the above tests should be discussed with an obstetrician or infectious diseases physician. Management of primary rubella or secondary re-infection depends on the gestation of the pregnancy and when the infecting occurred.

Pregnant contacts who are not immune should also be offered MMR vaccination after delivery.

Nil.

The routine use of immunoglobulin (IG) for post-exposure prophylaxis of rubella in early pregnancy is not recommended. It may be considered if termination of the pregnancy is not an option. Although IG has been shown to reduce clinically apparent infection in the mother, there is no guarantee that it will prevent fetal infection.

Rubella-containing vaccine does not provide protection if given after exposure to rubella. However, if the exposure did not result in infection, the vaccine would induce protection against subsequent infection. All women of childbearing age should be screened for rubella immunity and immunised if necessary.

Pregnant women should be screened antenatally. Those found not immune should be counselled to avoid contact with cases of rubella while pregnant, and should be offered MMR vaccination after delivery. See the Immunisation Handbook (Ministry of Health 2020) for further information.

Immunisation of a person who is incubating natural rubella or who is already immune is not associated with an increased risk of adverse effects.

Advise all contacts of the incubation period and typical symptoms of rubella. Encourage them to seek early medical attention if symptoms develop. Pregnant contacts may require additional advice; refer to an appropriate specialist.

Check for other cases in the community and look for associations. Also check any recent travel and possible outbreaks in areas visited.

Generally not needed. Clean and disinfect surfaces and articles soiled with upper respiratory tract secretions, urine or other infectious bodily fluids.

Medical officers of health are responsible for health education.

Ensure complete case information is entered into EpiSurv (external link).

If a cluster of cases occurs, notify the national protection clinical team (use Appendix 5: Escalation pathways for pathways for notification for awareness, or for escalation), and outbreak liaison staff at PHF Science, and complete the Outbreak Report Form.

• Communicable Disease Network Australia. 2019. Rubella case definition (external link). Australian national notifiable diseases case definitions (accessed 15 January 2021).
• Ministry of Health. 2018. Immunisation Handbook 2020 (external link). Wellington: Ministry of Health.