We performed a systematic sampling and analysis of airborne SARS-CoV-2 RNA in different hospital areas to assess viral spread. Systematic air filtration was performed in rooms with COVID-19 infected patients, in corridors adjacent to these rooms, to rooms of intensive care units, and to rooms with infected and uninfected patients, and in open spaces. RNA was extracted from the filters and real-time reverse transcription polymerase chain reaction was performed using the LightMix Modular SARS-CoV-2 E-gene. The highest occurrence of RNA was found in the rooms with COVID-19 patients (mean 2600 c/m(3)) and the adjacent corridor (mean 4000 c/m(3)) which was statistically significant more exposed (p < 0.01). This difference was related to the ventilation systems. As is commonly found in many hospitals, each of the rooms had an individual air inlet and outlet, while in the corridors these devices were located at the distance of every four rooms. There was a significant transfer of viruses from the COVID-19 patients' rooms to the corridors. The airborne SARS-CoV-2 RNA in the corridors of ICUs with COVID-19 patients or care rooms of uninfected patients were ten times lower, averages 190 c/m(3) and 180 c/m(3), respectively, without presenting significant differences. In all COVID-19 ICU rooms, patients were intubated and connected to respirators that filtered all exhaled air and prevented virus release, resulting in significantly lower viral concentrations in adjacent corridors. The results show that the greatest risk of nosocomial infection may also occur in hospital areas not directly exposed to the exhaled breath of infected patients. Hospitals should evaluate the ventilation systems of all units to minimize possible contagion and, most importantly, direct monitoring of SARS-CoV-2 in the air should be carried out to prevent unexpected viral exposures.