Indirect evidence – SARS, MERS
Overall, we included three retrospective cohort studies26,28,29 and 15 modeling studies that addressed KQ 1.30-44 The cohort studies used data from Beijing and Taiwan during the SARS outbreaks in 2003. The modeling studies used data from SARS and MERS outbreaks in Canada, China, Hong Kong, Japan, Korea, Singapore, and Taiwan.
One retrospective analysis of the SARS outbreak in Taiwan showed that out of 55,632 individuals quarantined due to contact with confirmed or probable cases, only 24 developed confirmed SARS (0·04%).29 The time from symptom onset to diagnosis was statistically significantly shorter in quarantined people (1·20 vs. 2·89 days, p=0·0061). The diagnosis-to-classification time (until people were officially classified as a SARS-case) was numerically shorter in quarantined people but not statistically significantly different (6·21 vs. 7·34 days, p=0·7864). 29
The modeling studies combined epidemiological data from SARS and MERS outbreaks with different community characteristics. Continuous-time or discrete-time compartmental models were used in addition to back-projection models and contact network models. Some studies considered multiple aspects of transmissibility, such as presymptomatic transmission, the contact intensity between individual people and households, the duration of infectiousness, and the host’s susceptibility to the infectious disease.
Overall, the modeling studies consistently reported that quarantine was an effective measure to control SARS and MERS outbreaks. One study provided estimates of the impact of quarantine based on data from the 2003 SARS outbreak in Taiwan, where more than 55 000 individuals were quarantined because of close contact with a confirmed SARS case.36 The average quarantine rate in Taiwan during the outbreak, however, was estimated to be only 4·7%. In other words, only one out of 21 asymptomatic individuals who should have been quarantined were indeed quarantined. Based on the authors’ model, an increase of the quarantine rate to 10% would have averted 214 SARS cases and 33 deaths; an increase to 60% would have averted 477 SARS cases and 80 deaths. Nevertheless, even the low quarantine rate of 4·7% prevented 461 cases and 62 deaths.36
Only three studies considered the effectiveness of quarantine in hypothetical examples that also modeled presymptomatic infectiousness.32,33,40 Day et al. used probabilistic models to determine the conditions under which quarantine is most useful.32 Their results indicated that the effectiveness of quarantine to reduce the number of infections depends on three main requirements: 1) that despite the implementation of isolation, a large disease reproduction number persists; 2) that a large proportion of infections generated by an individual could be prevented by quarantine; and 3) that there is a high probability (with a process in place such as case tracing) that an asymptomatic individual will be quarantined before he/she develops symptoms. In the second study considering presymptomatic infectiousness, Peak et al. found that the effectiveness of quarantine critically depends on the infectious disease’s biological dynamics (e.g., latent and infectious periods) and transmissibility. When the transmissibility is relatively low (basic reproductive number <2·5), quarantine can control a disease, even when infectiousness precedes symptoms by several days. When transmissibility is high, and symptoms emerge long after infectiousness, quarantine will be insufficient. Using a different transmission model, Fraser et al. reported findings consistent with those of Day et al.’s and Peak et al.’s studies.33

3.1.2 Resource use associated with quarantine

Two modeling studies assessed the resource use associated with quarantine.35 38
Gupta et al.35 compared the costs of two scenarios. In scenario A, SARS could be transmitted throughout the population without major public health interventions in place (only infected people are isolated). In scenario B, the early quarantine of first-degree contacts of the index case was implemented to contain the virus. The model used data from the SARS outbreak in Toronto, Canada. To assess the economic impact of both scenarios, direct costs (e.g., hospitalization, administrative effort) and indirect costs (e.g., lost productivity) were considered. Depending on the transmission rate (8%–25%), the costs of an epidemic without implementing quarantine vary. A transmission rate of 8% means that out of 100 contacts, eight get the infection; a transmission rate of 25% means that 25 contacts are infected. Aggregating primary, secondary, tertiary, and quartery infections results in 4,681 (with an 8% rate) to 406 901 infections (with a 25% rate). The direct and indirect costs of the disease would then range from 72 to 25 402 million Canadian dollars (reference year 2003). The authors concluded that at a transmission rate of 8%, the quarantine costs would range between 12·2–17·0 million Canadian dollars, depending on the timing with which the quarantine measurements were effectively implemented. The total savings varied between 279–232 million Canadian dollars. The earlier effective quarantine measures are implemented, the greater the savings are.
Mubayi et al.38 developed a general contact-tracing model for the transmission of an infectious disease similar to SARS. They performed a cost-analysis for various quarantine strategies combined with a fixed isolation strategy. In strategy I, a maximum quarantine effort at a per-capita rate independent of the number of infected cases is in place. In strategy II, the quarantine effort is proportional to the outbreak size, while in strategy III, the quarantine process depends on the outbreak size but is constrained by resource limitations. Contact tracing is assumed to happen randomly in the model, while in reality, this would depend on having contact with confirmed or suspected cases, so the model might overestimate the quarantine costs.
The authors recommend using a combination of quarantine and isolation. Although isolation alone might be sufficient to control an outbreak, it is too expensive and resource-intensive as isolation costs more than quarantine and it takes time to build isolation facilities. Therefore, a combination of quarantine and isolation is more beneficial than a single control measure. The optimal approach depends on available resources and the ability to quickly identify epidemiological factors, such as infectiousness or susceptibility during an outbreak to determine what quarantine and isolation combination is the best. Quarantine becomes less important the faster infectious patients are detected and isolated. Conversely, simulations show that the total cost is dominated by quarantine costs for a low contact-tracing efficiency and by isolation at a high contact-tracing efficiency. This means increasing the quarantine effort always results in lower overall costs over the entire outbreak. Strategy I was the most effective in decreasing the time to extinction but led to more cases, deaths, and people being isolated, though fewer were quarantined. Strategy II was the most cost-effective strategy when comparing the cost of achieving a unit of health benefit (e.g., reduction of a case) and the cost of the quarantine/isolation strategies. The authors stress that the greatest need for resources is early in the outbreak.
Table 3 summarizes the certainty of evidence for KQ1.
Table 3: Certainty of evidence ratings for the effectiveness of quarantine for individuals who were in contact with a confirmed COVID-19 case