Considering the fact that collected microbial aerosols remain on the filter surface, some possibility of their following detachment and re-aerosolization back to the gas carrier could not be neglected. The re-aerosolized particles could still be alive causing substantial risks for residents and environment. This issue could be addressed by adding disinfecting agents into the gas carrier or undertaking some inactivation procedures directly on the filter surface, making microbial particles inactive in the cases of potential re-aerosolization.

There are some technological approaches available for microbial disinfection. They include photocatalytic decomposition of microbes on titanium oxide surface irradiated by ultraviolet (UV; Vohra et al. 2006; Grinshpun et al. 2007), infrared (IR) radiation-based thermal decomposition (Damit et al. 2011), using chemicals directly injected into the air carrier or applied onto the filter surface (Pyankov et al. 2008; Huang et al. 2010), and others. Among variety of various disinfectants, some natural oils look promising due to low or nontoxic nature, especially in diluted form (Carson et al. 2006). During the last decade, a variety of essential oils from plants have been screened to assess their antimicrobial activity (Reichling et al. 2009).

The potential use of oils, such as tea tree oil (TTO) and eucalyptus oil (EUO), as disinfectants was clearly showed in recent in vitro studies regarding antibacterial (Wilkinson and Cavanagh 2005; Carson et al. 2006; Salari et al. 2006; Hayley and Palombo 2009), antifungal (Hammer et al. 2000; Oliva et al. 2003), and antiviral activities (Schnitzler et al. 2001; Cermelli et al. 2008; Garozzo et al. 2011). In addition, it was shown that essential oils are heterogeneous mixtures, with considerable batch to batch variation of constituents, depending on growth conditions at the plantations (Kawakami et al. 1990; Moudachirou et al. 1999). The antimicrobial activity of TTO is attributed mainly to terpinen-4-ol (35–45%) and 1,8-cineole (1–6%); however, other components such as a-terpineol, terpinolene, and a- and c-terpinene are also often present and potentially contribute to microbial disinfection (May et al. 2000). The EUO from different Eucalyptus species contains 1,8-cineole, a-pinene, and a-terpineol as major common compounds (Jemâa et al. 2012). A pharmaceutically graded EUO is commonly enriched up to 70% concentration of 1,8-cineole.

Recently, we suggested a technology based on coating fibrous filters by TTO, and reported the results of feasibility studies on the disinfection of bacteria (Pyankov et al. 2008) and fungal spores (Huang et al. 2010). In these studies, the TTO was used as both, filter efficiency enhancing media and disinfectant on bacterial and fungal aerosols captured on the filter surface. Considering current strong interest toward influenza related research, the present study is logical continuation of our previous investigations with the focus on the assessment of antiviral activity of essential oils (TTO and EUO) on inactivation of airborne influenza virus.

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