Varicella zoster or chicken pox is a highly contagious disease, the infection is serious in immunocompromised individuals, children and pregnant women. The causative agent is primary varicella-zoster virus infection (VZV), DNA virus from the Herpesviridae family. The only host for this virus is humans. The patients can transmit the virus 1-2 days before the rash happens and until the lesions crust (4–7 days after rash onset), with an incubation period of 10-21 days and an average of 14-16 days1. Worldwide, Chickenpox is seen mainly in the pre-school and school going children and <5% of adults are susceptible to varicella2. As of 2019, 18% of countries have introduced a routine varicella vaccination program, and an additional 6% have varicella vaccination programs for risk groups only2 In Oman, Varicella virus falls in group B diseases that needs to be notified within 7 days. In 2020 a total of (3045) cases, in 2021 (2385) cases and in 2022 (2860) cases were reported3. Varicella vaccination was introduced in 2010 for one-year old age group4. In 2022 a total of 78898 (98.6%) child was vaccinated (one dose) for Varicella3.
Establishing baseline policy for chicken pox outbreaks in schools in Oman, is essential to further understanding regional variations in vaccinations and associated risk factors with school age un-vaccinated children. This study will assist in developing public health policies and interventions for preventing, detecting, diagnosing, and managing atopic diseases to reduce their burden and improve patients’ quality of life.
We conducted an outbreak investigation in the Indian School Al Seeb as a response of the Department of Disease Surveillance and Prevention under DGHS Muscat, in order to contain the outbreak, treat the infected cases, and prevent further spread. It’s a case series study based on cases reported as confirmed between August-October 2023 epidemiologically linked and all studying in the Indian School AL Seeb. The place of infection is a public source it can lead to huge number of infections, making overwhelming pressure on the medical care system. The objectives are to control the current outbreak and to assess the severity and the extent of the current situation making sure no further chicken pox outbreaks occur in the future in the same location. Therefore, a descriptive study (case series) done for all positive chicken pox cases, found in the Indian school Al Seeb, in Muscat. Muscat is the capital of Oman with an aggregate population of 1,302,440 persons (2021) in which 58.3% of its residents are expatriates and 41.7% are Omani5.
On 22nd September 2023, the surveillance team from DGHS Muscat, noted some cases linked to a private school in Muscat governorate. On field investigation it was found that 47 cases were positively infected by chicken pox from the Indian school Muscat, among 3360 students and 148 staff.
We identified a total of 47 suspected cases of varicella (45 students, 2 staff) and none lab confirmed cases. All the cases underwent home isolation for 14 days with a regular phone follow up by the school nurse. Daily monitoring for all contacts during the incubation period (14 days) until the symptoms subsided (Figure 1). The mean age of cases was 5.63 years. 35.4% of cases were grade five students. All the infected patients were either Indians, Sri Lankans or Bangladeshi. 85.1%, 8.5% and 6.4% respectively. (Table 1)
All cases were epidemiologically linked: The incubation period ranged from 8-17 days (average of 14 days). A total of 19 contacts were reported from the family members of the students, no hospitalization reported among the contacts. 78.7% had a maculopapular rash, and only 61.7% had a fever. Vesicle formation was noted in only 12.8% of the cases. A total of 27 cases (57.4%) were not vaccinated and 20 cases (42.6%) were vaccinated with a single dose of varicella vaccine as the routine childhood vaccination. No pre-school vaccines were offered. The secondary attack rate was 1.4% (people got ill/people at risk). All cases recovered without any complications. (Table 2,)
Based on symptoms, incubation period, the epidemiological investigation, we found evidence of probable nosocomial transmission of varicella virus from person- to-person between the students and the staff (teachers and administrative staff) due to close contact. We recommend screening of exposed patients and staff, vaccination of those who have negative varicella serology or no vaccination history available and continuous follow-up until no new case appears for 42 days (2 incubation periods) after the rash onset of the last identified case to ensure that the outbreak has ended.
Table 1: The demographics of cases.
| Variables | ||
| Age | Mean | 10.5 |
| Median | 9 | |
| Minimum | 5 | |
| Maximum | 33 | |
| Gender | Male | 22 (46.8 %) |
| Female | 25 (53.2 %) | |
| Nationality | Indian | 40 (85.1 %) |
| Bangladeshi | 4 (8.5 %) | |
| Sri Lankan | 3 (6.4 %) | |
| Grade | 1 | 1 (2.1 %) |
| 2 | 1 (2.1 %) | |
| 3 | 3 (6.4 %) | |
| 4 | 7 (14.9 %) | |
| 5 | 16 (34 %) | |
| 6 | 2 (4.3 %) | |
| 7 | 3 (6.4 %) | |
| 8 | 9 (19.1 %) | |
| 9 | 2 (4.3 %) | |
| 10 | 1 (2.1 %) | |
| Division | A | 8 (17.0 %) |
| B | 11 (23.4 %) | |
| C | 15 (31.9 %) | |
| D | 2 (4.3 %) | |
| E | 6 (12.8 %) | |
| F | 3 (6.4 %) | |
| Designation | Student | 45 (95.7%) |
| Teacher (staff) | 2 (4.3%) | |
Table 2: Symptoms of the cases, vaccination status, related factor and the past medical history
| Yes | No | |
| Fever | 29 (61.7%) | 18 (38.3%) |
| Rash | 37 (78.7%) | 10 (21.3%) |
| Vesicle formed | 6 (12.8%) | 41 (87.2%) |
Figure 1: Epi-Week of the chicken pox cases in the private school.
References:
1. CDC. Chickenpox (Varicella). 2024 [cited 2024 Jul 9]. About Chickenpox. Available from: https://www.cdc.gov/chickenpox/about/index.html
2. Varicella / Chickenpox | CDC Yellow Book 2024 [Internet]. [cited 2024 Jul 10]. Available from: https://wwwnc.cdc.gov/travel/yellowbook/2024/infections-diseases/varice…
3. Departement of Information & Statistics Directorate General of Planning and Studies. Annual health report 2022 [Internet]. 2022nd ed. (2022).
4. Wahaibi ASAA, Al-Abri S. The feasibility of evaluating varicella vaccine effects in Oman using an electronic-based patient record system: a 5-year retrospective analysis. International Journal of Infectious Diseases. 2019 Feb 1;79:112.
5. eCensus Portal [Internet]. [cited 2021 May 24]. Available from: https://portal.ecensus.gov.om/ecen-portal/?lang=en