Rubella outbreak investigation, Gokwe North District, Midlands province, Zimbabwe, 2014 - a case control study

Introduction Rubella is a contagious disease, caused by rubella virus and transmitted via the respiratory route. Rubella in pregnancy may cause Congenital Rubella Syndrome (CRS), characterized by multiple defects to the brain, heart, eyes and ears. Gokwe North experienced an increase in rubella cases from 6 cases (24 June 2014) to 374 cases (12 August 2014). The study was conducted to determine risk factors associated with contracting rubella. Methods A 1:1 unmatched case control study was conducted. A case was a child <15 years, resided in Gokwe North, with maculopapular rash and tested positive for rubella specific IgM or was linked epidemiologically to a laboratory confirmed case. Blood was collected for laboratory diagnosis. An interviewer administered questionnaire was used. Epi Info™ was used to analyze data. Results Eighty eight cases and 88 controls were recruited, median age for cases was 7 years (Q1 = 4, Q3 = 8) and 6 years (Q1 = 3, Q3 = 9) for controls. Independent risk factors for contracting rubella were; classmate contact (AOR 9.44; (95% CI 4.29-20.77)) and having >3 children in a household (AOR 2.59; 95%CI (1.23-5.42)). Only 10.2% and 6.8% of the caregivers’ cases and controls respectively, knew rubella is spread through contact with an infected person (p = 0.57). Majority of caregivers (97.8%) reported to the health facility within two days of onset of rash. Conclusion Outbreak was driven by contact at school and was spread into the community through school children. Screening and isolation of the sick controlled the outbreak. Routine rubella vaccination could be considered to prevent similar outbreaks.

. About 5% of rubella infections occur in women of child bearing age and 90% of these women pass the rubella infection to their babies [1].
Worldwide it is estimated that there are more than 100 000 infants born with rubella syndrome each year [3]. In  Gokwe North District Medical Officer (DMO) and the local chiefs.
Written informed consent was obtained from study participants.

Descriptive epidemiology
A total of 374 cases of rubella were seen between the 24 th of June and the 12 th of August 2014 at Simchembu clinic, Gokwe North district. Six cases were laboratory confirmed and the rest were epidemiologically confirmed cases. Of these, 235 (63%) were females and 139 (37%) were males, showing a female to male ratio of 1.7:1. One hundred and two (27%) cases were under fives, one hundred and seventy seven (47%) cases were children in the 5-9 years age group, eighty nine (24%) cases were above 10 years and 6 (2%) were women of child bearing age. Gokwe North district, Wards 1 and 31 were affected by the rubella outbreak. One hundred and sixty six (44%) cases were children from Simchembu 1 Primary School and one hundred and seventeen (31%) cases were from Simchembu 2 Primary School. The highest risk of developing rubella was at Simchembu 1 Primary School with an attack rate of 16.6%, followed by Simchembu 2 Primary School with an attack rate of 11.7%. Figure

Analytic epidemiology
A total of 88 cases and 88 controls of children below 15 years were recruited into the study. Of the 88 cases 53% were males and 47% were females. Of the 88 controls, 50% were males and the rest were females. The median age of cases was 6.5 years (Q1=4; Q3=8) and of the controls was 5.5 years (Q1=1; Q3=9  Table 3).

Caregiver knowledge and perceptions on Rubella
Caregivers perceived the rubella illness as measles. All (100%) care givers perceived the illness as a dangerous disease and childhood immunization as important. Only 10.2% and 6.8% of the caregivers' cases and controls respectively, knew that rubella is spread through contact with an infected person (p=0.57). The majority of the caregivers (97.8%) reported to the health facility within two days of onset of rash and did not use any local herbs at home.

Epidemic preparedness and response
The

Discussion
The study sought to determine factors associated with contracting rubella in Gokwe North district using a case control study design.
This study design has a potential for ascertainment bias, which was

Study limitations
There was a possibility that controls could have been infected with rubella virus but not yet developed signs and symptoms of rubella during the investigation period. This could have introduced ascertainment bias which might have reduced the strength of associations; the median age for the cases was 6.5 years and for the controls was 5.5 years because the school going children in the community were mostly affected than the non school going children; caregivers perceived the rubella illness as measles and they were knowledgeable on measles which has some similar risk factors and signs and symptoms with rubella; no published case control studies on rubella were available; hence the author used unpublished studies; the study was conducted on children who were 15 years and below, hence the results cannot be generalized to populations outside this age group.