A report published in April 2020 by the European Center for Disease Control and Prevention (ECDC) highlights that the percentage of healthcare professionals infected by SARS-CoV-2 in Spain is the highest in the world with 20% of all reported cases, followed by Italy (10%), China (3.8%) and the USA (3%) . According to data from the Spanish Ministry of Health, 52,643 health workers had been infected on July 9, representing more than 22% of all infections . At the end of April, 237 workers from the ICU of our hospital were tested for detection of SARS-CoV-2 genome and antibodies by PCR and ELISA technique, respectively. All of them were negative suggesting a low circulation of the virus among these professionals.
Some experimental studies have reported that SARS-CoV-2 can remain viable in the air generated by aerosols for up to 3 h, and on surfaces of copper, cardboard, stainless steel, and plastic for 4, 24, 48, and 72 h respectively . Previous studies have also found other coronaviruses, such as SARS and MERS, in air samples within aerosols suggesting a possible air transmission . Guo et al.  analyzed environmental contamination in surfaces collected in several yards of a hospital in Wuhan, including an ICU with an air change rate of 16 cycles per hour (no equipment with negative pressure is reported). They found that the most contaminated surfaces were those that had frequent contact with the hands of workers and patients, such as computer mice, trash cans, sickbed handrails and door knobs. Furthermore, Guo et al.  found that virus was detected in 70% of the ICU floor samples and half of the medical staff’s shoe soles, suggesting a possible function of the shoes as carriers of the virus. Santarpia et al.  analyzed surface and aerosol samples collected in an isolation unit for asymptomatic or mildly ill patients and in a hospitalization area of the University of Nebraska Medical Center by RT-PCR for SARS-CoV2. Although the method of collection is not explained in the study, the virus was detected in a high percentage of personal objects such as mobile phones, television remote controls, personal computers or patient lenses, as well as on environmental surfaces such as bed rails, floor, vents, and medical equipment of patients with COVID-19 (pulse oximetry, nasal cannula, and incentive spirometer). Razzini K et al.  found SARS-CoV-2 RNA in 37 environmental samples. Viral RNA was detected in 35% and 50% of the samples obtained in the ICU and in areas considered semi-contaminated (undressing room), respectively. No viral RNA was detected in clean areas. Other authors also found environmental contamination in the air and surfaces of different hospital areas [16,17,18] in very different proportions (5–52% of the samples). Although Zhou et al. found viral RNA in 52% of the environmental samples in a London hospital, they could not grow the virus in Vero E6 and Caco 2 cells. This fact support that genome detection does not imply the viability and infective capacity of the virus . These authors also reported a surprisingly low environmental contamination in the ICU in relation to other hospital areas . Other studies also reported environmental contamination in towel bowl of the bathrooms suggesting that fecal shedding could be a potential route of transmission . Although these studies showed a significant environmental contamination in areas with COVID19 patients based on detection of RNA from SARS-CoV-2, no infection among health workers was reported, which is explained by the implementation of effective protection measures .
In contrast to these studies, Colaneri et al.  did not detect SARS-CoV-2 genome in environmental samples collected using moistened swabs in a hospital in Northern Italy. Such as the authors state, the low number of samples is a limitation of this study. Nevertheless, our results obtained by analyzing a higher number of samples (102 vs 16) support the no detection of SARS-CoV-2 RNA in environmental samples from hospital areas where patients with COVID-19 are attended. A possible limitation of our study is that the protocol cleaning, which was performed twice per day (morning and afternoon), influenced in the results. To avoid this limitation and given that SARS-CoV-2 can remain viable on surfaces between 4 and 72 h , samples were collected at different morning/afternoon hours within 15 days. Thus, the time from cleaning to sampling was variable. In any case, a possible explanation of the lack of environmental contamination could be a strict cleaning protocol with sodium hypochlorite, a high air change rate, and a negative pressure in the ICU. These facts together with the protection measures used could also explain the absence of contagion among healthcare professionals in our ICU.