Background: Measles is a highly contagious viral infection that can lead to serious complications and even death. We investigated to describe measles outbreak at a big detention center in Makkah, Saudi Arabia, from September to October 2021.The study aimed to assess the magnitude of the outbreak and to identify associated risk factors.

Methods: A descriptive followed by an unmatched case control study for 165 cases and 251 controls was conducted. A structured questionnaire was used to collect data from cases and controls. Cases were described by person, time, and place. Multivariate analyses were used to find independent variables linked to measles, and odd ratios and confidence intervals were calculated. Data was analyzed using Microsoft Excel and SPSS.

Results: We identified 165 cases (65% females), including one death and admission rate of 5.5%. Most of the cases were Ethiopian (89%), while the age group < 1 year was mostly affected (44%). In bivariate analysis, the risk of being infected with measles was 2.97 more likely in those who were not due for vaccination compared to those who had been vaccinated with measles vaccine (OR 2.9, 95%CI 1.4-5.7, P=0.04). Multivariate analysis found four factors to be independently associated with measles infection in this outbreak. Prior vaccination, (AOR 0.2, 95% CI 0.06-0.46, P = 0.001), being in detainee housing rooms 20–40 (AOR, 10.16, 95% CI 4.96-20.8, P = 0.001),Places of detention inside the kingdom before being transferred to prison were also significantly associated with the infection, particularly in Makkah (AOR 3.6, 95% CI 1.3-10.1, P = 0.01) and Al Madinah (AOR 10.9, 95% CI 1.04-115.5, P = 0.04).

Conclusion: Measles outbreak can occur in intense exposure settings like prisons. In this outbreak, mass vaccination campaign was crucial to control the outbreak, however crowdedness and high turnovers of detainees make the control of the outbreak difficult.