Heterogeneous

Apart from the incidence and mortality caused by it, Coronavirus disease (COVID-19) has had a significant impact on other diseases.

COVID-19 pandemic has variable influences on TB incidence and the number of deaths. On the other hand, the negative effects of health service disruption were observed to be dominant on the increase in number of deaths. If the treatment is successful, infectious individuals progress to long-term latent (\(L\)) and may transit to \({E}_{L}\) from \(L\) by relapse, reinfection, or reactivation with the rate, \(\tau\). When people in \({E}_{S}\), \({E}_{L}\), and \(L\) are treated, they move to the treatment group (\(T\)) by the number of preventive therapy (\(m\)) derived from literature reviews 24. Several studies suggest that TB mortality and incidence would increase in 2021 and coming years owing to the negative impact of COVID-19 8, 15, 18, 29. The fraction (\(q\)) of individuals in \(E\) progress to the infectious group (\(I\)), while the rest progress to the latent group (\(L\)). Patients in \(I\) stay with the unfavorable treatment proportion (\(p\)), or die from TB with mortality rate (d), derived from TB death reports 23. We expect COVID-19 to affect TB outcomes differently by age since the burden of TB and COVID-19 is higher in the elderly as compared to the young population. Model simulation predicted that TB incidence and deaths would decrease from 24,680 to 22,427 and from 1509 to 1036, respectively, over a period of next 6 years (Figs. 4, 5, S2, S3). This shows that TB-associated cases and deaths in Korea could continuously decrease if there was no COVID-19 hindering TB management. In the SEIL model, the population was classified into six groups based on the disease states: susceptible (\(S\)), recently infected (\({E}_{S}\)), at-risk-of relapse, reinfection, or reactivation (\({E}_{L}\)), infectious (\(I\)), long term latent (\(L\)), and treated among close contact and latent TB (\(T\)). Patients were assumed to be non-infectious during active TB treatment, and successful treatment gave people a similar level of relapse, reinfection, and reactivation risk to patients with long-term latent infections. Assuming that there would be delays in management of TB due to COVID-19, we developed a deterministic compartment model of TB transmission dynamics incorporating age structure to assess the impact of COVID-19 on TB burden. The burden of TB in the elderly is a challenging problem in South Korea, accounting for more than 45% of the newly diagnosed cases among them in the year 2019 19. On the other hand, the number of TB-related deaths mainly depends on the level of health service disruption for TB care. It was predicted that with a high degree of health service disruption, the number of TB-related deaths would increase up to 155 in 1 year and 80 percent of the TB-related deaths would be in the elderly population.