Rubella

Question 1

Routine rubella screening test and cut-offs

Answer 1

IgG only
-ve –> immunise post-partum
+ve 10-15IU/mL –> consider re-immunising post-partum
+ve >15 IU/mL immune

Question 2

When to test for rubella (IgG and IgM)

Answer 2

1. contact with rubella
2. rubella-like illnes (fever, erythematous rash, arthralgia), obtain serum 7-10 days after onset of rash

Question 3

When to repeat rubella serological testing

Answer 3

1. IgG +ve and IgM +ve (repeat in 2-3 weeks to confirm)
2. IgG -ve and IgM -ve but <3wks since contact, <7 days since onset of illness
3. IgG -ve and IgM +ve (could be false positive or not yet seroconverted)

Question 4

Risks with primary rubella at 1-12 weeks

Answer 4

• 80% fetal infection
• 85% congenital defects

Question 5

Risks with primary rubella at 13-16 weeks

Answer 5

• 54% fetal infection
• 35% congenital defects

Question 6

Risks with primary rubella at 17-22 weeks

Answer 6

• 36% fetal infection
• congenital defects rare

Question 7

Risks with primary rubella at 23-30 weeks

Answer 7

• 30% fetal infection
• congenital defects rare

Question 8

Risks with fetal rubella at 31-36 weeks

Answer 8

• 60% fetal infection
• congenital defects rare

Question 9

Risks with fetal rubella at >36 weeks

Answer 9

• 100% fetal infection
• congenital defects rare

Question 10

Rate of fetal infection with re-infection (Rubella)

Answer 10

<10%
CRS rare especially after 12 weeks

Question 11

Prenatal fetal diagnosis / testing for rubella

Answer 11

Rubella virus PCR or culture on CVS or amnio at least 6 weeks after known maternal infection. OR cordocentesis for rubella IgM.
BUT
- CVS can produce false positive PCR if contaminated
- PCR not widely avaiable and sensitivity not well validated
- False neg fetal IgM common until late in pregnancy

Question 12

Rubella period of infectivity

Answer 12

One week before until 7 days after rash

Question 13

Early manifestations of congenital rubella syndrome

Answer 13

1- Deafness (SNHL 60-75%)
2 - CNS dysfunction (10-25%, e.g. intellectual disability, DD, microcephaly)
3 - Cardiovascular defects (10-20%, PD, pulm a stenosis)
4 - Ophthalmological abnormalities (10-25%, cataracts, microophthalmos, retinopathy etc)
5 - Other (FGR, haem abn., GIT, pneumonitis, osteitis)

Question 14

Late manifestations of congenital rubella syndrome

Answer 14

1. Deafness (SNHL)
2. Neuro deficiencies, epilepsy
3. Retinopathy, cataracts
4. Tooth defects
5. Growth retardation
6. T1DM (50x risk), thyroid dysfunction
7. Panencephalitis