The effect of climbing chalk powder on the infectivity of human coronavirus OC43

There does not appear to be any studies in the published literature on the stability of SARS‐CoV‐2 in climbing chalk powder (magnesium carbonate and/or calcium carbonate), which has been hypothesized to pose a potential risk of fomite transmission of coronavirus disease 2019 (COVID‐19) within climbing gyms. The aim of this study was to determine the infectivity of a model human coronavirus HCoV‐OC43 in the presence of climbing chalk powder on a dry plastic surface. The stability of HCoV‐OC43 on a plastic surface dusted with climbing chalk powders (magnesium carbonate, calcium carbonate or a blended chalk) was determined by titration on BHK‐21 fibroblast cells. No chalk and no virus controls were included. HCoV‐OC43 was stable on the plastic surface for 48 h. The stability of HCoV‐OC43 was significantly (P ≤ 0·05) reduced in the presence of magnesium carbonate, calcium carbonate and the chalk blend; the infectivity was reduced by ≥2·29 log(10) 50% tissue culture infective dose (TCID(50)) immediately upon on contact and by ≥2·46 log(10) TCID(50) within 1 h of contact. These findings suggest that the infectivity of coronaviruses is reduced by climbing chalk, limiting the risk of potential fomite transmission.