Dear Editor In recent days, coronavirus disease (COVID-19) as a viral infection caused by the SARS-Cov-2 virus has become a pandemic disease and has created critical conditions worldwide . According to previous studies on pathogenic viruses associated with acute respiratory distress syndrome, each virus has a specific virulence dose, which it is about 2×103-3×103 viral particles for the influenza virus. Given the emergence of the SARSCov-2 virus and no complete information on its virulence dose, it is clear that its very low virulence dose can cause its rapid spread. Regarding the effectiveness of the use of simple cloth filter masks, it can be stated that these masks provide relative safety depending on their type and structure . In this regard, Blachere et al., reported that in multi-stage sampling of influenza viruses, 46% of the viruscontaining particles are trapped in the first filter layer of the sampler with a diameter of 4 microns, 49% of the viral particles are trapped in the second layer filter with a diameter 1 to 4 microns and only 1% of viruses are trapped in the last layer filter with a diameter of about 1 micron [2-4]. Coughing, sneezing, speaking, and breathing create a cloud of particles in the air with varying diameters ranging from a few millimeters to <1 micrometer. Large droplets (larger than 50 microns in diameter) are immediately deposited to the ground. Most respiratory droplets containing viruses are in this size range. Medium droplets (10 to 50μm) remain in the air for several minutes. Small particles (<10μm), including droplets nucleated by larger particles, can evaporate for hours and can be easily inhaled deep into the respiratory tract. On the other hand, the SARS-Co2 virus remains alive in the airborne aerosols for 3 hours [2, 4]. Therefore, the use of simple surgical masks for patients is necessary, especially during admission, to prevent the spread of large respiratory droplet released directly during coughing and sneezing and small droplets that are produced indirectly from the evaporation of the large droplets in the hospital environment. In addition, the use of ventilation systems can prevent the high concentration of these particles in hospital environments. In this regard, it is essential to educate hospital health experts about the necessity of using ventilation systems and their performance. On the other hand, the viability of viruses in the air is highly dependent on environmental conditions. Ambient temperature is one of the key factors influencing the stability of viruses in indoor air. In the case of the influenza virus, it has been reported that a temperature of 70˚C causes complete inactivation of the virus. Also, at 5°C, the viral transmission is significantly increased. While at 30°C, the viral transmission between hosts is obviously decreased. A recent study on the Corona viruses has reported similar results [2, 5]. Moisture factor is another factor influencing the transfer of viruses in the air. The lowest transmission rate occurs at low humidity and dry air (with a relative humidity in the range 20-30%), and the highest transmission rate occurs at high relative humidity (80-50%). Therefore, viruses can be prevented by monitoring and controlling the temperature and relative humidity in hospitals by using natural and mechanical ventilation systems to adjust the temperature and humidity at the appropriate level [2, 6]. According to World Health Organization (WHO) guidelines, it is recommended to use laboratory ventilation systems and if are available heating/cooling systems, fans/air conditioning units and local cooling system with laminar air flow can be used in diagnostic laboratories of hospitals. In this case, the velocity and direction of the air flow must be laminar to prevent turbulent currents. This point should also be considered in the case of natural ventilation . It is also recommended to use of biological safety hoods with HEPA filters that CAN trap 3 microns particles or larger with a 95% efficiency in diagnostic and research laboratories. These hoods are specifically designed for laboratory works on dangerous and respiratory viruses . If the laboratory is not equipped with a ventilation system and a suitable hood, transporting the sample to a reference laboratory instead of using several non-standard laboratories is recommended. For disinfection of hospital interior surfaces, the most effective disinfectants for inactivating viruses include alcohol-based disinfectants (ethanol), chlorine, and aldehydes. Savlon is a well-established antiseptic in Iran. This brand is actually a combination of two disinfectants of Chlorhexidine and Cetrimide. Sovlon is used in rapid disinfection of medical and surgical instruments, as well as surgeons' hand washing and wound cleaning. Its solution (1%) is also very suitable for disinfecting wounds and washing hand and body skin. It is a strong bactericidal, but has low effect on viruses. Two disinfectants that are effective on viruses include sodium hypochlorite and ethanol, which their minimum concentration and contact time should be considered to disable the virus. In a recent study on the SARS-Cov-2 virus, it was reported that the minimum concentration of sodium hypochlorite required to deactivate the virus was 0.21% with a contact time of 1 minute. Hydrogen peroxide is also an effective detergent with a minimal concentration of 0.5% and a 1-minute contact time for inactivation of the new coronavirus . Ethanol or ethyl alcohol in the range of 78-95% requires a minimum contact time of 30-60 sec to deactivate coronavirus types including SARS-CoV and MERS-CoV. However, a risk assessment is required for monitoring all hospital units and identifying critical points that have the potential to spread the infection to personnel, and planning and performing measures according to the WHO guidelines is necessary to reduce the risk of spreading the disease [4, 8, 9]. Considering the importance of prevention in the medical staff, it is recommended to educate these personnel by educational programs, especially hospital health experts.
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