Microbial inactivation by 222-nm far-UVC: a systematic review and dose-response synthesis in air, water, surfaces and biofilms

Background. Published 222-nm far-UVC efficacy values span orders of magnitude, but differences in exposure matrix, microbial state, dose measurement, shouldering, and tailing are often collapsed into a single "susceptibility" value. This systematic review mapped the evidence and assessed whether a pooled D90 could be estimated.

Methods. Retrospective systematic review of a selected corpus. We extended an initial 81-report dosimetry dataset and a 19-report targeted update with full texts recovered on 2 October 2026. Eligibility required a separable nominal 222±2 nm arm and viable microbial/infectivity outcome. Su and Sheng were included; Chen remained contextual and Liu a secondary review. D90 preserved model-specific logarithmic bases and full curves. Alternative Sheng fits were retained for sensitivity. Selection and extraction were AI-assisted and ratified by two reviewers.

Results. The integrated map contains 103 reports, 63 inclusions and 51 D90 conditions from six reports. The 57 model estimates include four alternate fits per organism in Sheng, not eight independent conditions. Su MRSA slopes yield D90 4.74 mJ/cm² (conditional transformed 95% CI 4.08–5.65) on bedsheets and 16.95 (14.08–21.28) on blankets. Sheng UV-only biphasic fits yield nominal D90 15.14 and 15.22 mJ/cm² for S. aureus and E. coli, without recoverable model covariance. The baseline McDonald complete model yields 8.30 mJ/cm² versus 1.86 for slope alone; four Petersen D90 targets remain unattainable under fitted plateaus. No coherent stratum met the meta-analysis criterion.

Conclusions. Preserving the complete curve changed D90 from 1.86 to 8.30 mJ/cm² for McDonald and identified four unattainable targets for Petersen. The synthesis explains differences between estimates through matrix- and model-specific comparisons; it does not establish a universal dose or clinical efficacy.