Model Answers Microbiology Written examinations 2007 - RCPA

Question 4. Write short notes on:
Norovirus detection
Role of anaerobic blood cultures
Flocked swabs
Non cultivable bacteria
Norovirus detection
+ss RNA virus; Calciviridae, human calici virus distantly related to the other human
calicivirus....sapovirus. 2 strains of Norovirus, genotype 1 and 2. Responsible for
acute gastroenteritis. Nausea 9%, vomiting 69% and diarrhoea 66%, abdominal
cramps 33% also headache, fever, chills reported. first recorded epidemic in 1968.
Norwark virus. Epidemics occur in winter and spring and low background disease
throughout the year. Often associated with hospitals, nursing homes, cruise ships,
restaurant s and schools. Virus shed in vomitus and faeces. Faecal oral and vomitus
oral eg alleged vomitus aerosol landing on food or fomites and then being consumed.
In developed countries 50% population infected by 5 th decade. Acquired earlier in
developing companies with poor sanitation. Gut virus receptor related to certain
blood group antigens. Blood group B individuals are resistant to infection. RNA
codes 3 ORF: ORF 1 encodes a non structural polyprotein that self cleaves to form 6
structural proteins. ORF2 the capsid protein; ORF3 a minor structural protein.
Diagnosis : RT-PCR of faeces or vomit. EM and IEM used in the past. Antigen
based tests available but have low sensitivity and do not cover all human strains of
norovirus probably due to antigenic variability/instability. (genotype 2 common
strain in Australia
Role of anaerobic blood cultures
Past blood culture studies have shown rates of anaerobic bacteraemia of 10-15%.
More recently this rate has fallen. ~5%. Finding anaerobes must be taken seriously
as they can indicate important underlying primary infection or underlying disease. B
frag = intraabdominal infection, F necrophorum + Lemmiere‟s disease or
necrobacillosis with venoocclusive complications, clostridial sp and association with
colonic cancer, gas gangrene. Often polymicrobial bacteria in gut disease.
Automated systems detect anaerobes at similar rates
Flocked swabs
Used for 2 reasons; > nasopharyngeal cells cp cotton tipped swabs or NPAs, better
detection of N gono and Chlamydia. Nylon, > absorbtive surface, non inhibitory
Non cultivable bacteria
Recent molecular tools suggest that non cultivable bacteria exist in many situations
such as the gut. These organisms do not yet grow on defined media. An example is