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