The prevalence of asymptomatic carriers of COVID-19 as determined by routine preoperative testing

Abstract

Background:

The coronavirus disease SARS-CoV-2 (COVID-19) has swiftly spread throughout the globe, greatly influencing all aspects of life. As in previous pandemics, concerns for limited resources and a sustainable medical workforce have been on the forefront of infrastructure modifications. Consequently, surgical specialties have needed to consider each surgical case for necessity and safety during the COVID-19 outbreak. At our institution, availability of SARS-CoV-2 assay has allowed preoperative testing of asymptomatic surgical patients.

Aim/Objective:

To better define the prevalence of asymptomatic carriers in a surgical population and to better understand the impact of testing on our personal protective equipment (PPE) supply.

Methods:

We began routine, preoperative testing for all asymptomatic patients coming to our academic medical centre on 30 March 2020. Scheduled surgeries were deemed urgent by the surgeon with a review for appropriateness by a novel surgical committee. A retrospective patient chart review was performed. Emergency surgeries were excluded. Asymptomatic patients with positive test results had their surgeries rescheduled at the discretion of the surgeon and patient. Patients who tested negative underwent surgery with staff using standard PPE.

Results:

Eighty-four asymptomatic surgical patients were tested preoperatively with three (3.6%) testing positive for SARS-CoV-2. Preoperative testing saved 498 N95 respirators over this time period.

Discussion:

This is the first report of routine COVID-19 preoperative testing in an asymptomatic surgical population. Within this population, there is a 3.6% rate of asymptomatic SARS-CoV-2 carriers. Through this practice, personnel exposure can be minimised and access to PPE can be preserved.

Background

The coronavirus disease SARS-CoV-2 (COVID-19) has already had far-reaching implications on our way of life. Analysis of pandemics in the past can offer guidance in response to this virus. Similar to the 1918 pandemic, there are many complex, often ethical, decisions to be made. Critical care capacity must be considered when deciding to triage major trauma and elective surgeries (Kass et al., 2008). Necessary resources to adequately care for patients with COVID-19 include a healthy workforce and a stockpile of medical equipment, including personal protective equipment (PPE). Consequently, individuals may be required to augment their use of PPE due to equipment constraints throughout multiple patient encounters, possibly leading to increased viral transmission. In addition, up to 40% of the healthcare workforce could be absent, as seen in previous severe pandemics, due to many factors such as infection, emotional toll and social circumstance (Paranthaman et al., 2008). Therefore, institutional measures must be established in order to preserve the infrastructure required to maintain the health system during the COVID-19 outbreak.

Transmission of COVID-19 is via respiratory droplets as well as direct contact with respiratory secretions. Through airway manipulation, aerosol generating procedures (AGPs) such as intubation lead to an increased risk for exposure (Ong and Khee, 2020). There have been many safety practices suggested to reduce transmission such as the induction of anaesthesia only in the operating room, presence of a reduced number of staff during AGPs and the use of increased protective gear. In response to the limitations in the availability of testing for SARS-CoV-2, the American Society of Anesthesiologists has stated the importance in using Tier 2 PPE (including N95 respirators) during AGPs for all patients, even those who are asymptomatic, during this time (Anesthesia Patient Safety Foundation, 2020).

Our medical centre embarked on a three-tier strategy heading into this pandemic: (1) practise social distancing and reduce exposure; (2) preserve PPE; and (3) increase critical care capacity. When considering this strategy in combination with the risk of asymptomatic carrier transmission, we quickly decided to initiate preoperative testing for any patient coming to our medical centre for a planned AGP, including intubation, and for whom we had 48 h advanced notice. Coincident to this decision was a process to actively reduce our surgical schedule through case postponement by nearly 80% in accordance with guidance issued by various professional societies, including the American College of Surgeons (American College of Surgeons, 2020). The aim of the present study was to document the prevalence of asymptomatic carriers of SARS-CoV-2 in the preoperative surgical population and to quantify its effect on PPE preservation.

Methods

We obtained institutional review board exemption for this study. Routine, preoperative testing for all asymptomatic patients coming to our academic medical centre was initiated on 30 March 2020. Surgeries being scheduled were deemed urgent by the surgeon with a review for appropriateness by a novel surgical committee. During the study period (30 March 2020 to 12 April 2020), patients were tested within 48 h of planned operation using the Abbott RealTime SARS-CoV-2 assay. A retrospective patient chart review was performed to obtain age, gender, co-morbidities, surgical indication and COVID-19 test results.

This process involved all outpatients having a scheduled procedure under general anaesthesia, monitored anaesthesia care or at risk of requiring an APG, being screened at a standalone COVID-19 screening clinic two days in advance of their procedure. Patients who tested positive were notified and case-by-case discussions ensued about whether to proceed with surgery. Patients in need of emergency surgery were excluded. Patients who tested negative underwent their procedure with all staff using standard precautions, Tier 1 PPE (standard surgical masks and gowns); hence, preserving scarce PPE such as N95 respirators. Our process for preoperative surgical testing is delineated in Figure 1.

Figure 1.

Flow diagram of surgery scheduling process during the COVID-19 pandemic.

Results

Eighty-four patients were included in this study with three patients testing positive for SARS-CoV-2. Of the three positive tests, 2 (66.7%) cases were further postponed. The singular case that proceeded despite testing positive was declared an emergency due to the patient’s clinical status. Eighty-one patients with negative testing went on to have their procedure with Tier 1 PPE. Table 1 shows patient demographics and Table 2 shows types of urgent surgeries being performed during this time period. Assuming the use of six N95 respirators per case (one for the attending anaesthesiologist, one for the resident anaesthesiologist, one for the attending surgeon, one for the resident surgeon, one for the circulating nurse and one for the scrub nurse), we hypothesise that preoperative testing saved 498 N95 respirators over this time period:

Table 1.

Preoperative patient demographics.

Total patients	84
Positive for COVID-19	3 (3.6)
Average age (years)	51.8
Gender
Male	40 (47.6)
Female	44 (52.4)
Average number of co-morbidities*	3.2

Values are given as n or n (%).

^*The most common co-morbidities encountered included hypertension, hyperlipidaemia, coronary artery disease, peripheral vascular disease and chronic kidney disease.

Table 2.

Types of urgent surgeries being performed.

Type of surgery*	Patients (n)
Otolaryngology	15
Ophthalmology	11
General/Breast	10
Orthopaedic	9
Gynaecology	9
Cardiac	6
Gastroenterology	6
Thoracic	5
Neurosurgery	4
Oncology	3
Vascular	2
Transplant	2
Urology	2

^*A laparoscopic appendectomy was postponed, while a finger mass excision and a laparoscopic hysterectomy with bilateral salpingooopherectomy were cancelled, due to positive preoperative tests.

Total N95s saved = 6 – N95 respirators/procedure × (81 procedures on COVID-negative patients + 2 procedures cancelled due to COVID-positive status) = 498 N95 respirators.

Discussion

This is the first report examining the role of routine preoperative SARS-CoV-2 testing to determine the prevalence and potential PPE implications of detecting asymptomatic carrier status in a surgical population. We have already found several benefits to testing this group. First, we may have spared the patients who tested positive from a higher morbidity, higher mortality surgical procedure associated to the relative immunosuppression that may result from SARS-CoV-2 infection (Wang and Zhang, 2020). COVID-19 can greatly complicate the perioperative course. The development of postoperative fever and pulmonary complications may pose a diagnostic dilemma and can result in a higher than expected mortality (Lei et al., 2020). Moreover, the relationship between the stress imposed by surgical procedures and transmission or exacerbation of current COVID-19 infection is not currently known. Additionally, it is possible that performing surgical procedures on asymptomatic carriers of COVID-19 may lead to operating room (OR) and instrument contamination, which may lead to transmission of the infection to the operative team (Aminian et al., 2020).

Second, we limited exposure of our staff to a potentially higher-risk mode of transmission associated with AGPs, such as intubation and the aerosols that persist in the room thereafter containing viable viral content (Van Doremalen et al., 2020). Researchers from China and Italy have identified a subset of asymptomatic patients that were potentially able to transmit SARS-CoV-2. Data from China approximate the asymptomatic carrier rate of COVID-19 at 5% (Tian et al., 2020). Based on this scenario, a small Italian village west of Venice enacted a widespread containment effort that included extensive testing policy and isolation of those with positive tests. Within 10 days, the number of sick patients from COVID-19 decreased from 88 to 7 (Day, 2020).

Third, we spared PPE, specifically N95 respirators, which allows for a greater availability of Tier 2 PPE. This intervention allows the healthcare workforce to remain protected and assists in further mitigating viral transmission. Lastly, the study sample encompassed a large age range, had a well-matched gender distribution and covered many surgical indications, demonstrating a group that is generalisable to the surgical population.

While this study is novel, it is not without limitations. Due to testing constraints and reduced surgical schedules to ensure adequate resources for COVID-19 patients, this is a relatively small dataset containing 84 patients in a two-week period. While the asymptomatic rate is lower than previously reported, the study group may not be reflective of the general population as the dataset only includes preoperative surgical patients at a tertiary referral hospital. Additionally, testing for the COVID-19 disease is presently limited in many areas of the country and this testing process may not be adoptable, especially in those healthcare regions that are limited in their testing abilities or are presently so overwhelmed that non-urgent surgeries are prohibited.

Furthermore, all testing modalities are subject to varying levels of accuracy. Although testing for SARS-CoV-2 has improved both quantitatively and qualitatively, the validity is a limitation that must be considered. Currently, the assay used in this study suggests a 95% detection rate for COVID-19 in vitro when the viral load is 100 copies/mL or more (Molecular.Abbott, 2020). In the clinical evaluation, although the sensitivity and specificity reported the same level of accuracy, the total number of patients tested was 91 (Molecular.abbott, 2020). Therefore, testing could have reduced accuracy when attempting to detect patients having a lower viral load but still able to transmit COVID-19, such as those at the start or end of their illness. Additionally, the SARS-CoV-2 assay is limited in that it detects RNA and not the live virus. Given the limited data on testing, negative results should be combined with clinical, geographical and epidemiological consideration when deciding whether to operate on a patient during this pandemic. False-negative test results may potentially expose healthcare providers as they will be exposed to AGPs without full PPE, including N95 respirators and appropriate eye and gown protection. Lastly, although it is our institution’s policy not to use N95 respirators on COVID-19-negative patients, it is still possible that individuals had access to N95 respirators and used them during the procedure. As this testing process’s quantitative impact in limiting exposure of COVID-19 to healthcare providers is presently unknown, future studies will need to be done to evaluate this important metric, especially if such a system for testing surgical patients preoperatively is to be widely adopted.

Conclusion

We report the first experience of routine COVID-19 preoperative testing in the asymptomatic surgical population at our institution. Within this population, there is a 3.6% rate of asymptomatic SARS-CoV-2 carriers. Through routine preoperative testing, personnel exposure to aerosolised virus can be minimised by reducing the risk of personnel using Tier 1 PPE on patients who, despite being asymptomatic, were actually COVID-19-positive. Moreover, access to Tier 2 PPE can be preserved in relation to personnel not routinely using N95 respirators, but rather having the ability to risk-assess whether Tier 1 PPE is sufficient based upon a negative result.