2021TrialShort answer

Q33 (f)

5 marks

Question

Rubella is an infectious disease caused by Rubivirus rubella. The disease is frequently mild, with a characteristic rash often appearing two weeks after exposure and lasting for three days. Other symptoms include fever, sore throat and fatigue, with joint pain common in adults. Up to half of infected cases are asymptomatic. Rubella is usually spread from one person to the next through the air via coughs of people who are infected. People are infectious during the week before and after the appearance of the rash. Only humans are infected. Once recovered, people are immune to future infections. In the early 1940s, Australian ophthalmologist Norman Gregg noticed a high incidence of congenital cataracts in babies whose mothers had suffered from rubella during pregnancy. It was then statistically shown that infection during early pregnancy may result in a miscarriage or a child born with congenital rubella syndrome (CRS). The main defects result almost exclusively from rubella infection occurring in the first 16 weeks of gestation and include deafness due to cochlea malformation, eye and cardiovascular defects and central nervous system damage leading to mental retardation. Rubella is preventable with a single dose of the rubella vaccine being more than 95% effective. When rubella vaccination became feasible around 1971, both the United States and the United Kingdom embarked on vaccination programs. In the United States, the strategy was to vaccinate infants, so that eventually the reservoir in childhood would be abolished. In contrast, the United Kingdom decided on a program of vaccinating adolescent girls. Both strategies were partial successes, in that CRS incidence began to decrease.

An alternative hypothesis for the mechanism is that some of the symptoms of CRS are due to maternal infection causing malfunction of the mother’s liver resulting in excessively high (toxic) levels of Vitamin A in the blood of both the mother and the developing embryo. Vitamin A is stored in the liver and is also found in the diet in cheese, dairy, liver and meat.
A group of unvaccinated pregnant women in a developing region has just been exposed to rubella virus.
Outline an epidemiological study that could be carried out ethically to test the Vitamin A hypothesis outlined above.

Uncropped source page 32 for question 33.f; requires human review and cropping — Reviewed visual · source page 32

Uncropped source page 35 for question 33.f; requires human review and cropping — Reviewed visual · source page 35

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Solution

Criteria	Marks
• Correctly identifies the type of study.<br>• Includes only patients under 16 weeks.<br>• Designs a valid investigation.<br>• Details a suitable method and analysis of results.	5
• Four of the above, one less well.	4
• Three of the above, two less well.	3
• Two of the above, less well.	2
• Provides some relevant information.	1

Additional guidance from the source:

[graph information:
Type of Circle any appropriate words: descriptive, analytic, experimental, epidemiologica observational, prospective, retrospective, cohort, case-control, cross- l study sectional, case, longitudinal, clinical trial, blind, double-blind Method of 1. Pregnancy of subjects dated using appropriate technology and study those > 16 weeks excluded from study 2. Remaining subjects tested for rubella infection/antibodies and interviewed about possible symptoms of rubella. Those without signs or symptoms excluded from study. 3. Remaining subjects randomly allocated to two groups. The control group maintained their normal diet. The experimental group were placed on a low-Vitamin A diet, but sufficient to meet the need to the woman and developing child. 4. Blood levels of Vitamin A monitored regularly for all subjects 5. After birth, children examined for CRS symptoms such as cataracts, deafness, heart and CNS defects What results Higher levels of Vitamin A in blood correlated with higher rate of birth would support defects the Vitamin A hypothesis ]

Range: 1-4; average: 2.7 Comments: most students who attempted this question went some way to designing a study, but had difficulty describing the study (unclear how much of this you are expected to know for the HSC). Some students also designed studies correlating rubella and CRS, which is fairly well established. A large number of students thought that if there was a control group, then the study was a case control, which is not true, and also quite hard to do for this particular situation. Nothing was said about the number of women in the study, but it is unlikely to be large. So, to help you decide what type of study it is: 1. Descriptive: time, place, person, no control vs Analytic which has control 2. Observational follows exposure and disease status vs Experimental follows effects of controlled exposure 3. Types of observational: a. Cohort: records exposure status then follows disease development, comparing unexposed to exposed. Longitudinal, repeated observations of the same variable. Can be prospective where participants are enrolled at the beginning of the study and then followed over time, or retrospective where the participants exposure and outcomes are recorded. b. Case-control: a group with the disease and a group without the disease are formed and previous exposures and compared c. Cross-sectional: sample of people enrolled and exposures and health outcomes are measured simultaneously d. Case: intensive study about an individual or group in real-world context 4. Example of experimental is a clinical trial with a controlled process for exposure which tracks over time to determine effects of exposure 5. Unblinded (all parties know information), Blinded: information which may influence the participants is withheld until experiment is complete (or longer), Double-blinded: two parties (generally participants and researchers/health professionals) are blinded to information.

Supplied marking guidance · human reviewed

Compare this with your working, not only your final sentence.

Syllabus alignment

Module 8 · Non-infectious Disease and Disorders

EpidemiologyEvaluate the method used in an epidemiological study.

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