The aim of this study was to assess the time course of changes in influenza virus infectivity on personal protective equipment used in healthcare settings. The results demonstrate that the virus TCID50 was relatively stable at a certain level on the surface of personal protective equipment after 8 h. However, after 24 h, while the HA titer remained at a relatively stable level in all samples, the TCID50 decreased to below the detection limit in all samples except the rubber glove.
The stability of the HA titer after 24 h seems to be explained by the inherent properties of virus-associated carbohydrates and proteins. Hemagglutinin, found on the surface of the influenza virus, is composed of sialic acid-binding polysaccharides [16
] and carbohydrates resistant to heat and dryness. Since the HA assay detects the red blood cell agglutinating ability of hemagglutinin, regardless of the presence of infectious influenza virus, the assay was able to detect HA even after 24 h. In contrast, virus-associated proteins necessary for the infectivity of influenza virus are susceptible to heat and dryness, and this susceptibility is likely to be the reason why the virus infectivity, as determined by TCID50
, was reduced over time.
Surgical masks and N95 particulate respirators are made from non-woven fabric and are used by healthcare professionals during patient examinations [9
] or by patients to prevent transmission of a virus [19
]. In our experiments, the virus maintained infectivity on the surfaces of the surgical mask and the N95 particulate respirator for at least 8 h. There have been no reports to date on the maintenance of infectivity of the influenza virus on non-woven fabric surface. However, Bean et al. [13
] reported that the TCID50
on the surface of a handkerchief and pajamas decreased to below the detection limit in 12 h.
We considered that a virus would dry on the Tyvek surface, a material used to manufacture medical gowns because these materials do not absorb water. We observed that under our experimental conditions, the virus maintained its infectivity for at least 8 h, but it was below the detection limit after 24 h.
In our study, a coated wooden desk and stainless steel were used as samples for comparison with personal protective equipment. In healthcare settings, these materials may be contaminated by droplets containing pathogens from patients [11
]. These materials, as well as Tyvek, do not absorb water. We found that the influenza virus maintained infectivity for at least 8 h post-virus application on the surface of these materials, without showing any decrease in TCID50
, subsequently falling to below the detection limit in 24 h. This finding suggests that the virus did not maintain its infectivity for 24 h, which is consistent with the results obtained from the samples of personal protective equipment. According to Bean et al. [13
], a laboratory-grown influenza A virus (A/H1N1) maintained infectivity for at least 24 h on the surface of stainless steel at a temperature between 27.8 and 28.3°C and 35–40% relative humidity, and TCID50
reached the detection limit in 48 h. During our study, the temperature of the laboratory was maintained at 25.2°C and 55% relative humidity. This humidity was slightly higher than that in the study conducted by Bean et al. [13
] and was less favorable for infectivity of the influenza virus [21
Rubber gloves are recommended as a standard public health precaution [23
] and are used for almost all procedures in healthcare settings [25
]. Under the conditions of this study, the TCID50
on the surface of the rubber glove remained at a relatively stable level for at least 24 h post-virus application. Future studies should focus on whether a virus maintains its infectivity for more than 24 h on the surface of rubber gloves under the same conditions. One possible mechanism for the infectivity of the virus being maintained on the rubber glove is that the surface of the rubber glove was hydrophobically treated, while the other samples were hydrophilic. The virus solution formed water droplets on the rubber glove and, as a result, the droplets became embedded in the protein of the egg used to proliferate the laboratory-grown influenza virus, consequently protecting the virus from drying out.
It is clear from the results of our studies that influenza virus contained in droplets is able to maintain its infectivity on the surface of personal protective equipment as well as on a coated wooden desk and stainless steel in medical settings for at least 8 h. However, on the surface of rubber gloves, the virus can maintain its infectivity for the relatively long time of 24 h. Accordingly, healthcare professionals should renew/replace personal protective equipment if they have been exposed to droplets from patients with influenza [26
]; however, in practice, personal protective equipment cannot be replaced for each patient. For example, during the severe acute respiratory syndrome (SARS) panademic, personal protective equipment could not be replaced for each patient for the simple reason that there was a shortage in the supply of such equipment and clothing [28
]. However, our findings suggest that caring for patients without an renewal or replacement of protective equipment may be responsible for cross-infection of influenza virus and, therefore, that a frequent replacement of personal protective equipment for each patient would prevent cross-infection. Since we have shown that the influenza virus maintains infectivity for at least 8 h on almost all surfaces, the disposal of personal protective equipment to prevent cross-infection after possible exposure to influenza virus is an important healthcare procedure.
This study has a number of limitations. First, the experiments were only conducted at one specific temperature and 55% relative humidity. This experiment should be conducted under various conditions of low temperatures and low humidity, such as those found during winter when an influenza pandemic is likely to break out. The second limitation is that our experiments did not assess the time course of changes in virus infectivity between 8 and 24 h. Therefore, the possibility cannot be ruled out that infectivity was lost in <24 h. The third limitation is that our experiments used a laboratory-grown influenza A virus, while a previous study conducted to assess the infectivity of the influenza virus showed that influenza virus mixed with human mucus maintained its infectivity on the surfaces of banknotes up to 17 days [29
]. On the basis of this latter finding, we hope to investigate the infectivity of dried influenza virus or droplets mixed with mucus on the surfaces of personal protective equipment. Since the amount of virus in droplets emitted from patients with influenza has not been reported in the literature, it is unknown whether the amount of virus in such droplets is equivalent to that in the virus solution used in our experiments. This issue remains to be elucidated in future studies. Further studies involving a larger number of samples are required to assess the validity of this study.
In conclusion, the appropriate exchange of personal protective equipment in cases of exposure to secretions and droplets, including viruses spread by patients, should be encouraged among healthcare professionals to prevent cross-infection of the influenza virus.