Introduction: The latest outbreak of COVID-19 in Malaysia emerged in early September and had two determinants. First, it involved incarcerated populations from four prisons located in Sabah, Kedah and Penang states. Second, the Sabah state by-election campaigns accelerated the spread of COVID-19 in the state and across the South China Sea into the west Malaysia. The emergence of multiple incarcerated clusters at different time points may shadow the real dynamics of transmission of COVID-19 in the community and lead to inaccurate interpretation and conclusion. The study aimed to reveal the real spreading pattern of COVID-19 by excluding incarcerated clusters in the modelling.
Methodology: We extended the susceptible-infectious-removed (SIR) model to include an additional class for non-isolated active cases, which was assumed to impel the transmission of COVID-19 in the community. The model was fitted to actual total and removed cases for estimation of duration of transmission and hospitalization. The parameters were then applied to model the transmission for COVID-19 in the community.
Results: The presence of incarcerated clusters shadowed the dynamics of transmission of COVID-19 with a lower reproduction number of 2.0. The proportion of non-isolated active cases increased slowly from 49.4% on 1 September 2020 to 60.3% on 8 October 2020. In the absence of incarcerated clusters, the dynamics of transmission of COVID-19 appeared differently with a higher reproduction number of 2.3. The proportion of non-isolated active cases increased tremendously from 22.1% on 1 September 2020 to 63.7% on 8 October 2020. The tremendous increase of non-isolated active cases impelled the dynamics of transmission of COVID-19 in the community following the Sabah state by-election campaigns and more inter-state travels.
Conclusion: The inclusion of incarcerated clusters shadowed the dynamics of transmission of COVID-19 in the community with a lower transmission rate, which might lead to wrong interpretation of the dynamics of transmission in the community.