Here, we studied the risk of incident SARS-CoV-2 infection among HCWs residing days and nights in quarantine hospitals, relying on detailed longitudinal data collected during the first wave of COVID-19 in Egypt. We found that most diagnosed infections (70%) occurred during what we defined as healthcare-associated outbreaks (as compared to isolated infections). We observed high variability in nosocomial incidence, ranging from 0.45 to 2.25 infections per 100 PD across the three hospitals. Using a model-based approach, we estimated the risk of both diagnosed and undiagnosed SARS-CoV-2 infections among HCWs, by hospital and by hospital unit (ICU and non-ICU). We further estimated that a substantial proportion of infections may have remained undetected, ranging from 45.0–59.2% across the three hospitals.
Our study design has several limitations. First, HCWs were screened using rapid serological tests before starting their working shifts. This may have allowed recently infected – and probably infectious – HCWs to start a working shift, as antibodies are detected by serological tests in less than 40% of infected individuals within 7 days since symptoms onset [13]. The Egyptian public health authorities’ choice of a protocol relying on rapid serological tests before working shifts was mainly driven by material constraints. Indeed, the use of serological tests as a diagnostic tool was and remains of particular interest in limited-resource contexts due to their lower cost, the minimal equipment required, and faster results, as compared with reverse transcription-polymerase chain reaction (RT-PCR) tests [14]. For this study, this may have led us to slightly underestimate the infection risks, as some HCWs may not actually have been at-risk. Second, the data collected for this study was scarce. The urge of implementing control measures under limited resources forced Egyptian hospitals to implement the quarantine-hospital strategy rapidly and, in some cases, during very short periods of time. Scarce data limits the strength and reach of our methods, and thus, our modeling choices were driven by parsimony. In particular, we assumed a constant overall risk of infection among HCWs over time, in each hospital unit, even though this disregards dynamic fluctuations in risk driven by variation in the number of HCWs and/or patients in the hospitals, as well as the frequency and nature of HCWs’ contacts during their working shifts. Indeed, explicitly modelling different transmission routes (patient-to-HCW vs HCW-to-HCW) would have required additional parameters in the model, leading to identifiability issues due to the scarcity of our data. In addition, this assumption allowed us to compare our results between hospitals and with existing literature on similar contexts or settings (see below). We would like to however stress the importance of developing modelling tools applied to low- and middle- income contexts, despite the difficulties that may come with limited resources. In particular, it is of great interest to evaluate what was the impact of interventions such as the quarantine-hospitals, which was implemented only in a few settings, to accompany future decision-making.
We found a ~ 5-fold higher observed risk for Hosp3 as compared with the risk found in Hosp1; whereas the risk of infection at Hosp2 was just slightly higher. The higher risk of SARS-CoV-2 infection we report for Hosp3 and the higher risk faced by HCWs assigned to the ICU of Hosp3 may be partly explained by the short period over which this hospital adopted the quarantine organization, which coincided with the country's highest epidemic activity of the first wave [4]. This may have led to a high proportion of severe and thus highly contagious COVID-19 patients referred to quarantine hospitals together with a higher workload for HCWs. Contrarily, Hosp1 adopted the quarantine organization in mid-March 2020, and thus experienced several weeks of lower epidemic intensity that may have improved preparedness for intense COVID-19 activity and implementation of infection control measures for invasive procedures (e.g., intubation in the ICU). Third, despite the quarantine strategy being adopted nationally, the differences between the organizations of each of the three hospitals (working shifts lengths, quarantine-organization period) should be accounted for when comparing risk estimates across the three hospitals. Data from other hospitals that have adopted a quarantine strategy will be beneficial to better understand occupational risks and eventually study the performance of such a strategy in comparison to standard care settings.
Our model-based approach, accounting for false-negativity rates of testing, as well as the right-truncation of our data, allowed us to estimate the risk of both diagnosed and undiagnosed SARS-CoV-2 infection among HCWs, by hospital and by hospital care unit. We estimated that a rigorous quarantine organization with systematic testing of HCWs at the end of their working shifts captures only about half of all HCW infections. Of note, the higher proportion of infections that remained undetected in Hosp3 (59.2%, versus 46.4% and 45.0% in Hosp1 and Hosp2, respectively) may be explained by the shorter duration of the working shifts (7 days), which may result in false-negative tests for HCWs infected a short time before the end of their shift. Moreover, these results suggest that in the absence of systematic testing at the end of quarantine working shifts, an even larger proportion of infections among HCWs may remain undetected, thus putting HCWs’ close contacts at risk of infection [15] and, consequently, putting themselves at risk for adverse psychological symptoms [16].
The model-based estimates we found for the SARS-CoV-2 infection risk in Hosp1 and Hosp2 are consistent with infection point-prevalence reported in earlier studies performed in non-quarantine Egyptian hospitals (varying from 4.2–14.3%) and with incidence estimates reported among front-line HCWs in the UK (13% infection rate after one month) [10, 11, 17]. For comparison, a summary of previous results obtained early in the Covid-19 pandemic and/or specifically in the Egyptian context is presented in Table 4. Moreover, our results suggest that HCWs assigned to non-ICU face a higher risk than those assigned to the ICU, in Hosp1 and Hosp2, which is in line with what was observed in previous studies addressing the occupational risk of SARS-CoV-2 infection for HCWs in non-quarantine settings [18]. Overall, our findings on Hosp1 and Hosp2 suggest that, providing sufficient preparedness, HCWs working in quarantine hospitals may not face a higher infection risk, and thus highlight the benefits of implementing a quarantine-hospital strategy.
Table 4
| Median estimated incidence rate per 100 PD (95% CrI) | Probability of infection for a 7-day shift (95% CrI) | Median number of SARS-CoV-2 infections (95% CrI) |
ICU | Non-ICU | Overall | All | Diagnosed | Proportion of undiagnosed infections |
Hosp1 | 0.59 (0.11–1.61) | 1.27 (0.68–2.01) | 1.05 (0.58–1.65) | 7.1% (4.0–11.0%) | 59 (45–74) | 31 (15–51) | 46.4% (18.8–66.7%) |
Hosp2 | 1.33 (0.33–3.33) | 2.75 (1.12–5.02) | 1.92 (0.93–3.28) | 12.7% (6.3–20.8%) | 31 (14–52) | 17 (7–31) | 45.0% (5.6–70.8%) |
Hosp3 | 9.37 (3.48–19.66) | 7.12 (2.06–18.71) | 7.62 (3.47–13.70) | 42.6% (21.9–64.4%) | 41 (19–63) | 16 (6–30) | 59.2% (34.8–78.8%) |
Comparison of the per-shift probability of infection estimated in Hosp1–3 with earlier estimates of the point-prevalence in other Egyptian studies and the observed cumulative incidence rate among HCWs in an English study. |
A notable strength of our study lies in the specific nature of the quarantine hospital set-up: because HCWs resided continuously in the hospitals over their entire working shifts, we were able to exclude risk of infection in the community and specifically quantify the nosocomial risk for HCWs. Conversely, results reported from non-quarantine hospitals worldwide are generally unable to distinguish between the nosocomial vs. community risk of infection. However, as most studies conducted in healthcare settings, we were unable to distinguish between patient-to-HCW and HCW-to-HCW routes of transmission. A previous study on several nosocomial Covid-19 healthcare-associated outbreaks in Germany reported that HCW-to-HCW transmission could represent an outsized risk as compared to the one due to infected patients [19]. Still, assessing the relative contribution between patient-to-HCW versus HCW-to-HCW SARS-Cov-2 transmission was left for future work. However, it is worth noting that during the outbreaks observed in our study, infections occurred in different care units, which may be indicative of HCW-to-HCW transmission, rather than simultaneous independent events of patient-to-HCW transmission. In early stages of the pandemic, personal protective equipment (PPE) placed a focus on the risk induced by patients, at times underestimating the risk of infection from –infected and undiagnosed– colleagues. Indeed, a modeling study based on a non-quarantine hospital setting found that the contribution of HCW-to-HCW transmission may highly exceed that of patient-to-HCW [20]. This may be especially true for quarantine hospitals in which HCWs share resting and conviviality rooms for longer times than in standard care settings. Adapting the use of PPE and social distancing between colleagues while ensuring sufficient social interaction and support to maintain HCWs’ mental health thus constitutes a specific challenge for quarantine hospitals [16].
In conclusion, the key role played by healthcare settings during pandemic waves since 2020 worldwide [21] highlights the need for innovative strategies to control the nosocomial risk. Quarantine hospitals, which effectively isolated non-COVID patients from COVID patients and allowed to closely monitor at-risk HCWs, may provide interesting solutions to this challenge. Our results suggest that, with sufficient anticipation and infection control measures, the risk faced by HCWs working in such quarantine hospitals can be brought down to levels similar to those observed in standard COVID-19 care settings. However, a comprehensive assessment of quarantine hospital care models should also include their impact on HCWs’ mental health as well as the potential benefits of earlier infection diagnosis, which is likely to reduce further hospital, household and community transmission [16].