Universal Masking to Control Healthcare-Associated Transmission of SARS-CoV-2

Objective: To assess extent of a healthcare-associated outbreak of SARS-CoV-2 and evaluate effectiveness of infection including masking Design: Outbreak investigation large-scale point-prevalence surveys We identified exposed patients and staff and classified them as probable and confirmed cases based on symptoms and testing. We performed a field investigation and assessment of patient and staff interactions to develop probable transmission routes. Infection prevention interventions implemented included droplet and contact precautions, employee quarantine, and universal masking with medical and cloth facemasks. Four point-prevalence surveys of patient and staff subsets were conducted using real-time reverse-transcriptase polymerase chain reaction for SARS-CoV-2. Results: The last was day universal 0 Covid-19, healthcare-associated Conclusions: Universal masking with medical facemasks was effective in preventing further spread of SARS-CoV-2 in our facility in conjunction with other traditional infection prevention measures.


Introduction
Since its emergence in China in December 2019, SARS-CoV-2 has caused an unprecedented global pandemic. [1][2][3] As of December 22 nd , 2020, nearly 18 million cases have been identified in the US alone. 4 While SARS-CoV-2 is known to spread person-to-person, exact modes of transmission remain debated. 5,6 A growing body of evidence suggests transmission occurs primarily via respiratory droplets.
Though studies showing viable viral RNA on shared surfaces and in smaller aerosols raise concerns for fomite and airborne transmission, 7,8 their contribution to overall spread of disease remains unknown. Amidst this uncertainty, many healthcare facilities have turned to universal masking protocols, in which most or all individuals entering a facility are required to wear a mask, as one means of preventing spread of SARS-CoV-2. 9,10 Previous small randomized controlled trials have demonstrated reduced transmission of respiratory illness after universal masking implementation within hospital units. 11,12 More recently, a meta-analysis of data from 39 studies of SARS, MERS, and SARS-CoV-2 outbreaks revealed a large reduction in risk of infection among exposed individuals using face masks or N95 respirators. 13 However, further data on facility-wide protocols is needed to assess the impact of universal masking on transmission within healthcare settings.
This paper describes infection control policies implemented in response to an outbreak of SARS-CoV-2 at a Veterans Affairs (VA) healthcare system, including institution-wide universal masking. We subsequently evaluate the effect of universal masking on healthcare-associated SARS-CoV-2 transmission using data from institutionally mandated point-prevalence surveys.
Identification of the Outbreak Our health system has two highly integrated facilities, with regular inpatient transfers and patient and staff travel between them. Facility 1 (112 beds) houses two intensive care units, a step-down unit, three general medical/surgical inpatient wards, and outpatient clinics. Facility 2 (218 beds) includes outpatient clinics, Community Living Center (CLC) units housing extended care, rehabilitation and hospice patients, spinal cord injury (SCI) units, and mental health units.
The index patient (Patient A) was a man with diabetes mellitus type 2 and an active cancer undergoing rehabilitation at Facility 2 following hospitalization at Facility 1. Patient A traveled regularly to Facility 1 for appointments at a procedural clinic. On day 1 of the outbreak, a staff member at this clinic returned to work after out-of-state travel with fatigue, cough, fever, and myalgia. This staff member was not wearing a mask or respirator at the time of interaction with Patient A. Several clinic staff members subsequently developed similar symptoms.
On outbreak day 7, Patient A developed fever and received intravenous antibiotics for a suspected urinary tract infection. A subsequent chest radiograph showed bilateral lower lobe interstitial infiltrates. After continued fever, he was transferred on day 9 to the emergency department at Facility 1. Blood cultures and a respiratory viral panel were negative. A nasopharyngeal swab for SARS-CoV-2 real-time reverse-transcriptase polymerase chain reaction (rRT-PCR) testing was sent to the state public health department, as in-house testing was unavailable. He was admitted to the COVID-19 rule-out unit on airborne and contact precautions. As he remained afebrile overnight without respiratory symptoms, the source of his fever was presumed to be catheter-associated urinary tract infection. He was transferred to a general inpatient ward on day 10 without isolation precautions. On day 13 his SARS-CoV-2 test returned positive and he was transferred to a designated COVID-19 ward. As he had been at Facility 2 for 22 days prior to symptom onset, his case was classified as healthcare-associated.
A second patient admitted on day 3 to the general inpatient ward (Patient C) developed cough on day 15. On day 18 he developed fever, prompting SARS-CoV-2 testing which returned positive that day. This was the second identified case of healthcare-associated COVID-19, and the first at Facility 1, prompting an intensive outbreak investigation.

Case Definitions
Exposure was determined by the presence of a known COVID-19 positive individual in a given facility location, with infectivity calculated using an incubation period of 1-14 days prior to symptom onset (or prior to first positive test if asymptomatic). Patients were considered exposed if they had an appointment at the procedural clinic during days 1-25 or were admitted to the general inpatient ward during days 10-40. Staff were considered exposed if they worked in the procedural clinic during days 1-25 or in the general inpatient ward during days 10-40. Patients and staff not in those locations but with unmasked contact with a confirmed positive case at either facility were also considered exposed.
Major criteria (subjective or measured fever, cough, shortness of breath) and minor criteria (chills, fatigue, myalgias, headache, anosmia, sore throat, gastrointestinal symptoms, imaging demonstrating bilateral infiltrates) were determined based on Centers for Disease Control and Prevention (CDC) guidance and early descriptive reports of disease from China. 14-16 Cases were deemed "probable" if they met two major criteria or one major and one or more minor criteria, regardless of testing status, or "confirmed" if they had a positive SARS-CoV-2 rRT-PCR. Due to limited testing supplies, we were unable to test asymptomatic patients and staff outside of the point prevalence surveys or unless necessary for transfer to an outside facility.

Chart Review, Contact Tracing, and Field Investigation
Patient medical records were reviewed and cases classified according to the definitions above.
Clinical data on symptom onset, exposures, testing results, and outcomes were compiled using REDcap (Research Electronic Data Capture) tools hosted at the Veterans Health Administration (VHA); REDcap is a secure, web-based software platformed designed to support data capture and management. 17,18 Staff exposed to confirmed cases were excluded from work for 14 days after last known exposure and asked to self-quarantine at home while monitoring symptoms.
Staff symptom and testing data were obtained from the institution's Employee Health department. Most likely routes of transmission were reconstructed, assuming an incubation period of 1-14 days. 19 Physical spaces involved in the outbreak (procedural clinic, support staff gathering area, and an inpatient room where multiple transmission events occurred) were investigated and relevant measurements obtained.

Interventions
Infection prevention policies were implemented in response to increasing community prevalence of COVID-19 and the Facility 1 outbreak ( Figure 1). Throughout the outbreak, community case counts increased from roughly 50 new cases/day on day zero to a peak of 1600 cases/day on day 26 and remained around 1000 cases/day after day 38. Eleven days before the outbreak, nursing staff at both facilities began screening inpatients for COVID-19 symptoms. Visitor screening at CLC and SCI wards began 7 days prior to the outbreak, with closure to nonessential visitors 5 days prior. Screening at Facility 1 and 2 entrances began on outbreak day 4; employees were temperature screened only, while patients and visitors were also asked about respiratory symptoms. Inpatients and new admissions who screened positive and had a COVID-19 test sent remained on droplet and contact precautions until results were available or an alternative diagnosis was identified. All visitors to both facilities were restricted beginning day 12.
On day 13, the inpatient COVID-19 screening algorithm was broadened to test all patients with fever, new cough, or shortness of breath plus one minor symptom listed above, and droplet and contact precautions could be discontinued only with a negative COVID-19 result. Beginning day 18, all tested patients were placed on droplet and contact precautions upon testing regardless of result. Universal masking among staff was implemented on day 22 with medical masks required for patient interaction and cloth masks for use at all other times, including in offices, lobbies, etc.
The policy was extended to outpatients and visitors on day 25. Eye protection was permitted but not mandated throughout the study period. All new admissions were tested starting day 50.

Surveillance
Infection Prevention maintained a database of tested patients within our healthcare system as required for public health reporting. Employee Health maintained similar data on employees.
Patient cases were defined as healthcare-associated if symptoms began >72 hours after admission. All cases not meeting this definition were considered community-acquired. Employee cases were defined as healthcare-associated if symptoms began within 1-14 days after unmasked workplace exposure to a known COVID-19 positive case.
We conducted four point-prevalence surveys on patients and staff beginning on day 33 (Table 1). Surveys 1, 2, and 4 were performed in response to VHA directives requiring screening for CLC and SCI patients and staff at Facility 2; these did not include Facility 1.

Outbreak:
Across Facilities 1 and 2 from days 1-40, 14 confirmed cases of healthcare-associated COVID-19 occurred among 250 exposed individuals (191 patients, 41 staff). Of these, 9 were linked to the general inpatient ward and 3 to the procedural clinic. The index patient was associated with both areas and with a separate staff member who provided support services (Figure 2). Thirty probable cases were identified (20 patients, 10 staff) of which 18 tested negative for COVID-19 and 12 had no testing. We identified no transmission links between probable cases and confirmed COVID-19 cases. While an additional 27 patients with community-acquired COVID-19 were admitted during the study period, we found no transmission links from these individuals in our review of records.
Among confirmed and probable cases of both patients and staff, 90.7% experienced fever, cough or shortness of breath (Table 3). Mean incubation period was 5.6 days (range 1-14 days). Mean length of follow up from last potential exposure was 18 days (range 0-41 days).
All transmissions occurred among patients and staff with direct interactions or close proximity without use of medical or cloth masks, N95 respirators, or other personal protective equipment (PPE). Transmission between patients C, D, E and staff 8 occurred within one inpatient room with an approximate area of 174 ft 2 (16m 2 ) and a maximum distance of 9.1 ft (2.8m) between beds. Though able to room three patients, the room had only one or two patients assigned throughout this period. None of the positive patients underwent aerosol-generating procedures (e.g., continuous positive airway pressure therapy, nebulizer treatment, etc.). The earliest date of potential transmission was day 1. The latest potential dates of staff-to-patient and staff-to-staff transmission were days 22 and 25, respectively.

Surveillance
System-wide surveillance identified 40 COVID-19-positive patients admitted to our facilities during days 1-65 ( Figure 1). Six healthcare-associated cases were identified during this period, of which 4 met our definition of exposed. Two additional cases from the outbreak were tested at outside facilities and identified outside of system-wide surveillance. The remaining two healthcare-associated cases occurred after implementation of universal masking and were unrelated to the outbreak. These cases were admitted on days 29 and 34 and neither had epidemiologic links to the outbreak locations or cases. One developed symptoms 5 days after admission, and one was asymptomatic and tested 5 days after admission for discharge purposes. All potentially exposed staff were masked, and none developed symptoms or confirmed disease.
Three exposed patients subsequently tested negative for SARS-CoV-2.
Point-prevalence survey results are summarized in Table 1 20 There was no spread between individuals in different rooms sharing one air handling system or in the direction of air flows out of rooms with infected patients (e.g. to hallways). Of the two healthcare-associated cases that were not part of the outbreak, neither were ever on the same floor as the outbreak ward, in the procedural clinic or in an area sharing air handling systems with COVID-19 positive patient rooms.
All roommate pairs were positioned more than 9 feet apart and were immobile with limited if any use of the shared bathroom. Though 6 feet is a frequent cutoff for physical distancing, the CDC's 2007 Guideline for Isolation Precautions notes the upper limit of droplet transmission is unresolved and may occur as far as 10 feet from the source. 21 Contamination of shared equipment or insufficient hand and environmental hygiene are other possible contributors to transmission, but our data raise concern that 6 feet may be insufficient to prevent transmission between unmasked individuals with prolonged exposure in an enclosed space, consistent with known transmission characteristics of SARS-CoV and newer data on SARS-CoV-2. [22][23][24] Early infection prevention interventions were insufficient to prevent or halt this outbreak. Daily inpatient screening was limited by variable application and inconsistent patient responses.
Employee temperature checks began on day 4, but not all infected persons experience fever, and even those who do may have afebrile intervals. The results from Survey 2 clearly demonstrate infected employees were missed. In-house COVID-19 testing became available on day 14 but was initially limited to fewer than 5 tests per day. It had minimal impact on healthcare-associated transmission despite a 1-hour turnaround allowing rapid isolation of infected patients.
The intervention best correlating with the end of the outbreak was implementation of universal masking on day 22, the last potential date of transmission from staff to patient. As of this date, all staff wore medical facemasks during patient contact and a cloth or medical facemask within the facility. One medical facemask was typically worn per shift on inpatient wards. Respirators were worn only on COVID-19 wards, and access outside of those units was extremely limited.
While a broadened inpatient screening algorithm and droplet and contact precaution policy for tested patients may have also contributed to outbreak control, multiple patients involved in the outbreak were not symptomatic or otherwise tested until after their transfer off the ward, and inunit transmission continued after these policies were in place until the implementation of universal masking.
Within the study period, there were no documented transmission events of SARS-CoV-2 involving patients or masked staff after implementation of universal masking, despite increased testing capacity and stable community prevalence. While two cases met our definition of healthcare-associated COVID-19 after universal masking implementation, neither was epidemiologically linked to another positive patient or staff. One patient developed symptoms 5 days after admission, the median estimated incubation period for COVID-19, suggesting possible infection prior to admission. 25 The other had no symptoms and also may have been infected prior to admission. Neither case resulted in a transmission event.
Multiple point-prevalence surveys found no cases among inpatients in either of our facilities even though five staff members from Facility 2 tested positive, suggesting that masking may have prevented transmission from healthcare workers to patients in our facility. The lack of contacts between positive staff also indicate masking may have been effective in preventing employee-to-employee transmission.
Our data have several limitations. This observational study includes multifactorial interventions and therefore cannot definitively prove the effectiveness of masking alone. We were unable to confirm transmission sources via viral genetic analysis, thus some transmission may have occurred through alternative routes than those proposed. Due to resource limitations, we did not audit compliance with the universal masking policy. Finally, point-prevalence surveys were separated by 1-2 weeks and could have missed asymptomatic transmission events. However, we detected no symptomatic transmission events during these periods.