Rubella

Question 1

What viral family is rubella in?

Type of virus (Baltimore)?

How many serotypes/genotypes?

Reservoir?

Answer 1

Togavirus (Rubivirus genus)

Enveloped +ssRNA (IV)

1 serotype, 12 genotypes

Human only

Question 2

What gene is used for rubella sequence typing?

Answer 2

E1

Question 3

Rubella basic reproductive number?

Answer 3

R0 = 3-8

Highly transmissible but fairly close contact required despite airborne transmission route

Question 4

Can rubella reinfection occur?

What are the clinical symptoms?

What implication does this have in pregnancy?

Answer 4

Yes, symptoms usually milder or more commonly asymptomatic

Reinfection during early pregnancy can still cause CRS, but risk is <10%, due to this if significant contact has occurred testing should be performed regardless of MMR history

Question 5

Infectivity period of rubella?

Answer 5

One week before to 4 days after rash (rash in pregnancy says 10 days post rash)

Question 6

Clinical symptoms of rubella infection (not congenital)?

Differential diagnoses?

Answer 6

> 50% asymptomatic

Mild prodrome - low grade fever, malaise, coryza, mild conjunctivitis

Lymphadenopathy followed by rash mostly behind ears, on face and neck and is transient

Differentials = B19, measles, HHB6, enterovirus, travel related viruses, GAS, Kawasaki, drug reaction

Question 7

Complications of rubella infection (not congenital)?

Answer 7

Thrombocytopaenia

Encephalitis

Arthritis and arthralgia

Question 8

Diagnosis of rubella infection (not congenital)?

Answer 8

RT-PCR in respiratory secretions

IgM and IgG in serum - all positive IgMs require confirmation at VRD (2x formats, RNA and avidity)

IgM shoud be positive from 3 d - 4 weeks post rash

Question 9

Risk of congenital rubella infection in pregnancy by week of infection

Answer 9

Pre-natal = no risk
<11 weeks = 90% risk of CRS
11-16 weeks = 20% risk of CRS
16-20 weeks = minimal risk of deafness only
>20 weeks = no risk

Question 10

Management of pregnancy in confirmed rubella infection

Answer 10

Managed based on risk assessment (gestation at infection, immunity) rather than foetal investigation

TOP should be offered if high risk of CRS

Question 11

Investigation at birth for babies born with ?CRS or maternal rubella infection during pregnancy

Answer 11

Cord blood, placenta, urine and oral fluid > VRD

Diagnosed based on IgM in serum or oral fluid or RNA detection at any site

Question 12

Management of exposure to rubella in pregnancy

Answer 12

Also investigate for exposure to B19 and measles

If documented rubella IgG positive or 2x MMR reassure (however if significant contact has occurred in first 16 weeks then investigation should occur due to reinfection risk)

If susceptible, test for IgM and IgG and collect blood 4 weeks later for seroconversion

Advise MMR post partum

(in susceptible individuals with significant exposure and where TOP is not an option, HNIG can be offered to reduce vireamia and potential extent of foetal damage but this does not reduce risk of foetal infection)

Question 13

Symptoms of CRS?

Differential diagnosis?

Answer 13

Classical triad = deafness, cataracts and cardiac complications

Cataracts and eye defects
Deafness
Cardiac abnormalities
Microcephaly
IUGR
Inflammatory lesions of brain, liver, lung and bone
Thrombocytopaenia
Petechial rash

Differential: Congenital CMV/Toxo/syphilis/VZV/HSV, enterovirus

Question 14

Management of neonate with CRS

Answer 14

Isolation at delivery as highly infectious for up to 1 year

Isolation at all appointments thereafter until non-infectious (2x negative THS and urine 4 weeks apart)

Management of symptoms

Question 15

Protective titre of rubella IgG?

Answer 15

10 IU/ml

Question 16

PEP for rubella infection?

Answer 16

None - MMR response does not develop quick enough to be used for PEP (but every opportunity to vaccinate is an opportunity!)

HNIG not indicated (except in niche situations in pregnancy)