Table 1: Characteristics of rubella, parvovirus B19 and varicella-zoster virus infections in the UK

Proportion susceptible in young adult females

1-2%

40-50%

10%

Infectivity - risk transmission from close contact (household attack rate)

High(90%)

Medium (50%)

High(70-90%)

Risk of intrauterine transmission by(gestational age)

11-16 weeks - 55%
>16 weeks - 45%

5-16 weeks - 15%
>16 weeks - 25-70%, increasing with gestation

28-36 weeks - 25%
>36 weeks - 50%

Risk of adverse fetal outcome

11-16 weeks - 20%
16 -20 weeks minimal risk of deafness only
>20 weeks - no increased risk

Congenital varicella syndrome:

Risk of adverse outcome for mother

Arthritis

Arthritis

Pneumonitis. Case fatality rate for mother estimated at 1/1000 infections in pregnancy

Available Interventions and benefits

Termination of pregnancy

Fetal hydrops - intrauterine transfusion reduces odds of death to 0.14

ZIG to mother and neonate attenuates

illness. Aciclovir within24 hrs of rash onset for mother. Aciclovir for infected neonates

Incubation period

14-21 days

13-18 days

14-21 days

Infectivity period (days pre and post rash onset)

7 days pre to 10 days post onset of rash

10 days pre to day of onset of rash

2 days pre onset of rash until cropping has ceased and all lesions crusted

Number of infections in pregnancy

Currently rare

1 in 400 pregnancies (ref 18) or seroconversion of 1.5 -13% per annum among susceptible

Exposure use of VZIG- 590-785 women per year, 1996-1999, England and Wales

Estimate 2-3 infections per 1000 pregnancies or 2000 maternal infections per year

Terminations of pregnancy

1995-96 - 18
1997 - 2

Unknown - not recommended

Unknown

Babies with congenital infection (proven)

1994-96 - 20
1997 to date* - 1

Unknown

Unknown

Babies with congenital damage (proven)

1994-96 - 19
1997 to date* - 1

Unknown

Unknown

Babies with congenital infection (estimate)

Rare (see text)

See below

30 neonates at risk of severe neonatal infection per year in UK

Babies with congenital damage (estimate)

Rare (see text)

2-8 fetal hydrops per 100,000 pregnancies (14-56 cases per year in UK ) 12-48 per 100,000 spontaneous abortion (84-336 cases per year in UK )

10 per year, England and Wales