Deposition of respiratory virus pathogens on frequently touched surfaces at airports

Ikonen, Niina; Savolainen-Kopra, Carita; Enstone, Joanne E.; Kulmala, Ilpo; Pasanen, Pertti; Salmela, Anniina; Salo, Satu; Nguyen-Van-Tam, Jonathan S.; Ruutu, Petri

We used a PCR panel employed in our standard respiratory virus surveillance to detect viral nucleic acid in the samples. We did not attempt to recover live viruses by cell culture. Although PCR methodology has limitations because it does not demonstrate the presence of infective virus, it is commonly used to detect the presence of a virus. Also limiting is that the total number of samples taken is relatively small (n = 94). Our sample collection took place within three hours of the daily traffic peaks, well within the reported survival times on surfaces associated with common respiratory viruses. However, whilst the Ct values in our study are similar to those for surface samples in other studies, e.g. [17] , these are relatively high, suggesting a low viral load on the surfaces that tested positive, and possibly not constituting the minimum infective dose. Likely due to the high Ct value, subtyping for the influenza A positive specimen was not successful and did not provide information on the origin of the viral strain and its epidemiological context. Alternatively sampling and recovery techniques may have been relatively inefficient, giving an illustration of the potential for transmission, but underestimating the true transmission potential of contaminated surfaces and air. Data concerning the infectious dose specifically for indirect contact are lacking [17] . Killingley and colleagues used a logical argument to conclude that their level of influenza A surface contamination on its own did not represent an infectious dose [17] . The reasoning was that as the copy count in their surface samples approximately only equated to that needed for aerosol transmission, and the likelihood that higher counts are required for indirect transmission, their surface contamination doses would not have been infective. In this study Ct values were similar to Killingley et al. [17] , so likewise it is reasonable to conclude that the environmental contamination we identified may not always (or ever) have constituted an infective dose. However, we are unable to determine precisely when each surface became contaminated, and therefore cannot exclude a higher viral load at an earlier time point. Likewise, we cannot establish the efficiency of our sampling technique and the readouts we have may be low due to sampling and recovery techniques. Notwithstanding, we establish the potential for virus transmission from several surfaces. On that basis we do not feel that the potential for transmission can be satisfactorily excluded based on our data.