The average size of pathogenic microorganisms expressed in nanometers is:

  • Viruses:  (including the average size of the coronavirus is 113nm)
  • Bacteria: 1000-10000nm
  • Yeast: 5000-30000nm
  • Fungi: 2000-100000nm

Viral pathogens are 3 to about 500 times smaller than bacteria, but lack a cell wall, possibly facilitating the penetration and absorption of UVC radiation.

Scope of deactivating the effective dose of UVC D90 radiation for bacteria, acc. to 253 results of the tests carried out in 1929-2009 range from 1 J/m² to 10,965 J/m², with the median effective dose being 28 J/m².

The scope of the deactivating effective dose of UVC D90 radiation for viruses, acc. to the results of hundreds of tests, ranges from 1 to 4480 J/m², while the median value of the results of 129 studies conducted in 1944-2008, analyzed in “A Genomic Model for Predicting the Ultraviolet Susceptibility of Viruses”, is 80 J/m². 


It should be noted that microbiological tests for inactivation of viral and bacterial pathogens in laboratory conditions are performed using different methods and in different environments.

The research carried out over 80 years was conducted in the water environment (especially viruses), in the air (in aerosols) and on surfaces. On the example of test results for the Escherichia coli bacteria or Coliphage φX-174 virus, a statistically lowest required inactivating effective dose of UVC radiation (of the same pathogens) is observed for tests performed in the air, a higher dose is noted for tests performed on surfaces and the highest statistically required dose is observed for tests performed in the aquatic environment.      

Tests performed on surfaces are carried out on carriers, i.e., in solutions and organic suspensions, e.g., on agar medium – these solutions show a very high absorption of the applied UVC radiation, which results in much lower irradiation of the tested pathogens, which are deeper inside the sample. Under non-laboratory conditions, their deactivation (for example on inanimate surfaces or in the air – in aerosols) requires an even lower dose of UVC radiation.