Measles Outbreaks in the Republic of Congo: Epidemiology of Laboratory-Confirmed Cases Between 2019 and 2022.

Abstract

In Africa, measles epidemics are frequently reported, despite numerous preventive measures, such as vaccination, which targets children under 5 years of age. Unfortunately, the Republic of the Congo is not an exception to this major health concern. Indeed, many cases are reported annually. Here, we provide an overview of the epidemiological characteristics of laboratory-confirmed measles cases from January 2019 to October 2022 as well as the risk factors associated with the occurrence of measles outbreak. Samples from suspected measles cases were collected across the country and sent to the National Laboratory of Public Health for confirmation. Specific IgM was tested using the enzyme-linked immunosorbent assay (ELISA). Data were analyzed using descriptive and analytic statistics (p < 0.05 was statistically significant). A total of 1330 samples were collected and analyzed. Over those 4 years, 537 samples were confirmed to be positive (40.3%) but with important disparities between years. A relatively low frequency of cases was reported in 2020. Overall, a progressive and significant evolution of positive cases was observed between 2019 and 2022, increasing from 16.8% in 2019 to 65.9% in 2022 (p < 0.0001). We report a low vaccination rate among children (44.8%) and a significantly high positivity rate in this group (46.6%) (p < 0.0008). No difference was reported according to the completeness of the vaccination scheme (p=0.094). Females were slightly more exposed to this infection than males (p=0.04; adjusted odds ratio [aOR]: 1.25 [1.01-1.6]), with an increased risk of exposure in rural areas (p=0.0001; aOR: 0.41 [0.32-0.53]). The department of Pointe-Noire had the highest positivity rate, while three other departments were considered high-risk areas: Likouala (p = 0.0001; aOR: 3.18 [1.80-5.61]), Pool (p=0.0001; aOR: 2.90 [1.70-4.95]), and Brazzaville (p=0.0005; aOR: 0.52 [0.36-0.75]). This study calls for strengthening the epidemiological surveillance system and vaccination strategy in the country. It remains important to research factors that induce a high positive rate among vaccinated children by biological verification of the immunization.