Comparing the bactericidal effect of ultraviolet germicidal irradiation between two time exposures against Bacillus subtilis on personal protective equipment

Ray Angelo B. Monje, Mariel Patricia P. Capuno, Manolo V. Hernal III, Maria Margarita M. Lota


Background: In the time of the COVID-19 pandemic, the use of personal protective equipment (PPE) as an infection control measure is recommended for healthcare settings to prevent the spread of the virus.
However, given the increased demand for PPEs worldwide and the limited resources available in the country, supply shortages are experienced by many healthcare facilities and workers. Furthermore, most PPEs should be discarded after use and may only be reused under emergency situations. Thus, the study sought to determine how to maximize PPE usage.

Objective: The study aimed to compare the effect of Ultraviolet Germicidal Irradiation (UVGI) against Bacillus subtilis between 30 and 40-minute periods. Specifically, the study targetted to establish if there is a difference in the mean percent reduction in CFUs of B. subtilis between that of the 40-minute and 30-minute treatment group of N95 FFRs and coverall suits.

Methodology: The study is a secondary research which builds upon the experimental results of the
commissioned study conducted by the Department of Medical Microbiology (DMM), College of Public Health, University of the Philippines Manila researchers to conduct data analysis. Furthermore, the PPE evaluated were coverall suits and N95 filtering facepiece respirators. They inoculated a total of 30 samples with B. subtilis for each type of PPE and subjected them to UVGI treatment in 30 and 40-minute periods. This study then employed inferential statistics, particularly a two-sample independent t-test, to further analyze the data from DMM and assess the difference between the two UVGI exposure durations on PPE decontamination.

Results: After calculating and analyzing the data using OpenEpi, the mean percent reduction was statistically greater (p-value = <0.0000001, α = 0.05) in the 40-minute exposure than the 30-minute exposure. The mean percent reductions of the N95 respirators were 98.68% and 99.41% for the 30 and 40-minute exposures, respectively. On the other hand, the mean percent reductions of the coverall suits were 80.40% and 99.71% for the 30 and 40-minute exposures.

Conclusion: Based on the significant difference in bacterial reduction between the two time exposures, the longer UVGI time exposure was more effective as a disinfectant. The results of the study contributed to knowledge on infection control using UVGI and its possibility as a method of decontaminating PPEs.


UVGI; B. subtilis; N95 FFRs; coverall suits

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Print ISSN: 2704-3517; Online ISSN: 2738-042X