The matrix was submitted to the surveillance team and expert evaluation at the end of the first month. With an online survey method, the question "How many of the ten contacts do you think each matrix classifies correctly?" was asked. The matrix received an average score of 8.6/10 (min: 8.2, max: 9.0) and was used in 1169 risky contact interviews in two months (24 August - 23 October 2020).
Three main headings came to the fore in health care workers contact risk classification.
- Differences caused by the ventilation of the environment: Indoors, well ventilated indoors, outdoors (figure 1)
Indoors are more risky areas where it is difficult to keep the distance between people wide . Another possible situation that increases the risk is the longer stay together indoors . Well ventilation, essential for a healthy indoor climate, helps limit the spread of the SARS-CoV-2 virus . However, according to available data, the contamination potential is much lower outdoors than indoor environments, due to the turbulence levels found outdoors . In evaluating the contact of HCWs with COVID-19 cases, it was necessary to categorize the contact environment as closed / well ventilated indoor / outdoor. However, in situations where the same environment is shared, the risk is associated with many factors including ventilation of the environment, use of masks, distance and exposure time .
SARS-CoV-2 spreads between people who are in close contact with each other. A distance of at least 1 meter is recommended for COVID-19 patients to reduce the risk of infection when talking or coughing . However, there are also sources that suggest staying at least 2 meters away from other people even in open environments . In contact risk assessment, it is important to take into account that a physical distance of at least 1 meter reduces the risk of SARS-CoV-2 transmission, but 2 meters may be more effective, and the greater the distance, the more likely to be protected .
The risk of SARS-CoV-2 spread is determined by how closely the interaction with the COVID-19 case takes places and how long this interaction lasts.. For healthcare workers, high-risk exposures are directly related to face-to-face contact lasting 15 minutes or longer [6,13]. Using the 15-minute contact time limit on the basis of evidence provides practicality in classification of contact risk . It should also be taken into account that the cumulative exposure time in repeated contacts affects the risk of transmission .
The mask worn by the person acts as a simple barrier to help prevent respiratory droplets from getting into the air and other people. The use of masks is particularly important in environments where people are close to each other or where social distance is difficult to maintain . Mask use details of both the HCW and the patient are important in determining the risk of COVID-19 exposure .
- Direct contact or material sharing
A high-risk contact occurs when healthcare workers care for COVID-19 patients without or with inappropriate PPE. If hand hygiene has not been achieved after direct contact with the patient, with the patient's body fluids, or with the patient's contaminated environment, it is also within the scope of high-risk contact . This feature becomes more important when the case in contact is a colleague, so many different items likes pens and keyboards could be shared with the case in the two days before the symptoms or diagnosis.
- Aerosol generating procedures (AGP)
Situations such as exhaling, singing, coughing, and sneezing create high-momentum gas clouds containing respiratory droplets. This moves droplets faster than background ventilation streams and they can reach distances of more than 2 meters in a short time . Some procedures performed on patients are more likely to generate higher concentrations of infectious respiratory aerosols than coughing, sneezing, talking or breathing . Performing aerosol generation procedures in healthcare settings or potentially elsewhere in closed, crowded, poorly ventilated environments increases the risk of infection . High risk contact can be considered when a healthcare worker is applying the procedure or is present in the environment without PPE or with inappropriate PPE during an AGP . The Ministry of Health's Assessment of the Contact Status of the Health Care Worker with the COVID-19 patient recommends the use of N95 masks and face shields or eyeglasses together in aerosol-generating procedures, considering the use of a medical mask instead of N95 or not using a face shield/eyeglasses as medium risk .
However, there are difficulties in determining whether the reported transfers during AGPs are due to aerosols or other exposures . Another issue is that currently there is insufficient evidence to support the effectiveness of face shields for resource control. Therefore, face shields are not currently recommended to replace masks .