Model Answers Microbiology Written examinations 2007 - RCPA

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Hepatitis B 1. Detect potential foetal infection and damage High risk groups Areas of high prevalence Household contacts of carriers Multiple sexual partners Tattoos, body piercing If HBsAg negative offer vaccination post partum Ensure screening and vaccination of family members Sag pos+ eag - - vertical transmission 5-20% Sag+ eag+ - vertical transmission 70-90% 90% of infected infants become chronic carriers 2. Sensitive and specific reliable assay available Yes: HBsAg; if positive HBeAb HBeAg LFT‟s and DNA if abnormal LFT‟s 3. Availability of a safe effective intervention strategy if detected No need for C/S HBIg (0.5ml) and HBV vaccine (0.5ml imi) Breast feeding: - although detectable HBV DNA in breast milk – no added transmission risk demonstrated 4. Occurs at a frequency that has a cost benefit for the screening Note that universal screening recommended as earlier attempt at identifying a risk group was not successful Hepatitis C 1. Detect potential foetal infection and damage If mother HCV Ab pos and HCV RNA PCR negative – prenatal transmission 0% If mother HCV Ab pos and HCV RNA PCR positive – prenatal transmission 0% Coinfection with HIV – prenatal transmission 9-45% Transmission proportional to RNA load 2. Sensitive and specific reliable assay available Yes HCV Ab – but need to confirm with a second assay with different antigenic matrix: RIBA may be useful to sort out in determinates or discordant serology Also HCV RNA/PCR viral load 3. Availability of a safe effective intervention strategy if detected No clear evidence re mode of delivery and reduction of perinatal transmission Breastfeeding: no increased risk of transmission demonstrated Most uninfected infants HCV Ab negative at 12 months Follow up infant HCV Ab at 12-18 months Or if concerned earlier HCV Ab and HCV RNA PCR If infected LFT‟s and HCV RNA PCR Refer for possible therapy (IFN and Ribaviron) 4. Occurs at a frequency that has a cost benefit for the screening Detection allows evaluation of treatment in the mother post partum
CMV VZV HSV 1. Detect foetal damage or well being of the mother Leading cause of congenital infection; (0.3- 2%) of live births Approx 6/1000 pregnancies Diagnosis: 40-50% risk of transmission Symptomatic disease 10% (normal 10%; sequelae 90%) Asymptomatic disease 90% (normal 90%: sequelae eg deafness 10%) 2. Sensitive and specific reliable assay available – limitations Asymptomatic v infectious mononucleosis syndrome IgM EIA 75% sensitivity and specificity May persist for months or years after primary infection Reappear with reactivation or reinfection False positives – other herpes viruses, pregnancy, autoimmune disease Serial rise in antibody levels v seroconversion v avidity May require ultrasound (30-50% sensitivity; Amniocentesis PCR +/- foetal serology 3. Availability of a safe effective intervention strategy if detected None effective for either prevention of transmission or for effective treatment of congenital CMV 4. Occurs at a frequency that has a cost benefit for the screening Risk groups Day care workers – seroconversion 11% per annum Parents with child in day care – 20- 30% per annum General population – 2-3% seroconversion per annum 1. Detect potential foetal infection and damage CVS 20 weeks – isolated case reports – zoster in infancy 2. Sensitive and specific reliable assay available Yes for wild disease No for past vaccination status VZVIgM; also VZV PCR for acute diagnosis 3. Availability of a safe effective intervention strategy if detected Passive immunisation VZV IgG < 96 hours Acyclovir to protect mother from severe varicella zoster not necessarily the foetus T2 Underlying lung disease Immunocompromised Smoker 4. Occurs at a frequency that has a cost benefit for the screening Common – however 90 +% immune; increasingly likelihood of varicella vaccine immunity 1. Detect potential foetal infection and damage
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Model Answers Microbiology Written examinations 2007 - RCPA

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