Gu et al. \cite{Gu_2022} reported on transmission of Omicron variant of SARS-CoV-2 in a quarantine hotel involving two infected individuals from the same floor with no history of direct contact. Airborne transmission across the corridor was suggested as a likely mode of transmission. Interestingly, Taiwan has recently reported several clusters of infections in quarantine hotels with similar suggested routes of transmission.In one instance, a cluster of seven cases was identified in a Taoyuan quarantine hotel; all cases had matched S gene sequence \cite{control,jessica-marlowtaiwan-covid-hoteloutbreak-dec2021}. Except for a single case with 1 vaccine dose, all others were fully vaccinated (2 with a high-end mRNA vaccine). No evidence of direct contact between cases was identified. six cases stayed in neighboring rooms on the same floor; one case stayed two floors above. The presumptive index case first experienced symptoms on date of arrival and was admitted to the hospital 2 days later. The dates of the first episode for all other cases were ≥3 days apart. Moreover, though they were tested later, higher Ct values were exposed.The subsequent epidemiological investigation suggested environmental exposure as a source of infection with several possible routes of transmission. Food collection was suggested as one risk factor similarly to \cite{Gu_2022}. However, the commonly shared ventilation system was suspected as another risk factor as one case was identified on a different floor.Though all recent clusters reported in Taiwan have been attributed to the Delta variant, and outbreaks of Omicron variant are yet to be encountered, the described situation has already prompted higher alert from the government: Taiwan has strengthened measures for operation of quarantine facilities and instructed more frequent testing of inbound travelers, increasing the number of required tests from 3–4 to 6–8 over a 21-day observation period \cite{hotels}.Conflicts of interestThe authors declare no conflicts of interests.

The study of Lee et al. \cite{Lee_2024} estimated the risk of incident tuberculosis (TB) in those diagnosed with latent TB infections (TBI) following screening. Under the current program in the Republic of Korea, only those under the age of 65 with TBI are recommended to undergo TB prevetive therapy (TPT), which is covered by national health insurance.  However, despite this provision, the incidence rate of active TB among those aged over 65 was five times higher than those under age 65, sparking vigorous debate on whether insurance coverage for TPT should be extended to all age groups. Lee et al. suggested that TPT might be less effective in reducing the risk of TB incidence among those aged over 60 (60+), with estimated adjusted hazard ratios (HRs) above one, albeit insignificant (Figure 1 in \cite{Lee_2024}). However, the interpretation of this finding requires caution. Considering the significant impact of comorbidities on increasing the risk of TB, individuals with comorbidities are more likely to be assigned to TPT and more likely to develop TB (Table 3 in \cite{Lee_2024}), suggesting that the presence of comorbidity serves as “confounding by indication” (Fig. 1) \cite{Kyriacou_2016}. While the study attempted to address this issue through multivariate adjustment, residual confounding \cite{Vansteelandt_2014} may persist, particularly when there is a notable imbalance in the comorbidity distribution between TPT recipients and nonrecipients. Specifically, the distribution of individuals with comorbidities within each age group, which is lacking in (1), may skew toward the TPT group, particularly among 60+, who are known to have a higher prevalence of comorbidities than the younger population. In this scenario, the multivariable adjustment, heavily relying on model extrapolation with limited empirical information on the TPT effect among those without comorbidities, might not fully mitigate confounding factors \cite{Vansteelandt_2014}.