To better understand the underlying mechanisms of aerovirology, accurate sampling of airborne viruses is fundamental. The sampling instruments commonly used in aerobiology have also been used to recover viruses suspended in the air. We reviewed over 100 papers to evaluate the methods currently used for viral aerosol sampling. Differentiating infections caused by direct contact from those caused by airborne dissemination can be a very demanding task given the wide variety of sources of viral aerosols. While epidemiological data can help to determine the source of the contamination, direct data obtained from air samples can provide very useful information for risk assessment purposes. Many types of samplers have been used over the years, including liquid impingers, solid impactors, filters, electrostatic precipitators, and many others. The efficiencies of these samplers depend on a variety of environmental and methodological factors that can affect the integrity of the virus structure. The aerodynamic size distribution of the aerosol also has a direct effect on sampler efficiency. Viral aerosols can be studied under controlled laboratory conditions, using biological or nonbiological tracers and surrogate viruses, which are also discussed in this review. Lastly, general recommendations are made regarding future studies on the sampling of airborne viruses.

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Methods for Sampling of Airborne Viruses

A simple method to screen cilantro and parsley for fecal indicator viruses.

Bacteriophages as Fecal Indicator Organisms

Researchers have recently renewed interest in bacteriophages. Being valuable models for the study of eukaryotic viruses, and more importantly, natural killers of bacteria, bacteriophages are being tapped for their potential role in multiple applications. Bacteriophages are also being increasingly sought for bacteriophage therapy due to rising antimicrobial resistance among pathogens. Reports show that there is an increasing trend in therapeutic application of natural bacteriophages, genetically engineered bacteriophages, and bacteriophage-encoded products as antimicrobial agents. In view of these applications, the isolation and characterization of bacteriophages from the environment has caught attention. In this review, various methods for isolation of bacteriophages from environmental sources like water, soil, and air are comprehensively described. The review also draws attention towards a handful on-field bacteriophage isolation techniques and the need for their further rapid development.

An Appraisal of Bacteriophage Isolation Techniques from Environment

The relationship between various indicator organisms and the presence of enteric viruses in treated drinking water, surface water and groundwater has been the focus of numerous investigations in the recent years. Faecal indicators have been found to be useful for pointing out the potential presence of enteric viruses in various water sources. Commonly used indicators include bacteria (e.g. E. coli, enterococci and Clostridium perfringens spores), and bacteriophages. The most appropriate indicator is one that can provide information about the presence of viruses in groundwater or surface water sources or the removal/inactivation of viruses by conventional water treatment processes. Bacteriophages can be recovered and detected by many different techniques, and numerous promising approaches are still in the developmental stage. It should be noted, however, that meaningful and universally accepted guidelines for the recovery and detection of bacteriophages in water environments are still underway.

Bacteriophages as faecal indicators in environmental systems: Historical perspectives and recent uses

Air quality within and around confined animal housing operations is important from both occupational exposure and environmental quality perspectives. Appropriate sampling equipment should be available so that bioaerosols are adequately characterized in terms of their component microbial populations. In this study the efficacy of a commercially available impaction-based bioaerosol sampler (SAS-100) was evaluated in terms of its ability to detect male-specific coliphages within and around poultry broiler houses. In addition to the manufacturer recommended agar medium, cellulose and cellulose-acetate filter media were also used as the collection surface. The agar medium and the cellulose ester filters provided very high recoveries of phages as compared to the cellulose filter (P<0.05). There was a wide range of recoveries ranging from 0–100% when the cellulose acetate filter was used to detect phages in bioaerosols within and around broiler houses. The results suggest that the sampler is capable of concentrating male-specific coliphages from bioaerosols. However, further studies are still needed to accurately determine the collection efficiencies of viruses.

Isabel Y. Espinosa

Papers

Impaction‐based sampler for detecting male‐specific coliphages in bioaerosols