Bacterial aerosols during colonoscopy: something to be worried about?

The surgeon Joseph Lister (1827 – 1912) was the first to see the role of “minute particles suspended in [the air] which are the germs of various low forms of life,” in the origin of wound infections that were frequently seen in compound fractures but not in simple fractures [1]. Pasteur had shown that exposure of a boiled fermentable fluid to air did not cause fermentation as long as no particles from the air could settle in the substances. These famous experiments with the swan-neck flasks brought an end to a long debate about spontaneous generation and showed that particles in the air and not miasmas were responsible for infection [2]. Somewhat later these minute particles or germs were named bacteria. Lister developed the carbol spray and antiseptic surgery to prevent the sedimentation of bacteria in wounds, and as a result he changed the fate of surgical patients dramatically [3] [4].

Since the work of Pasteur and Lister, air has become a well recognized medium of transmission of microorganisms. Microorganisms are brought into the air by shedding of scales and hairs from humans and animals, by whirling of dust, and by aerosols. Aerosols are clouds of droplets of different sizes. Aerosols are produced during talking, sneezing, and coughing, by cooling towers, bubble baths, showers and, according to the publication of Vavricka et al. [5], during the removal of a biopsy forceps during colonoscopy. The size of the droplets in an aerosol determines how far the aerosol can spread; large droplets cover short distances, small droplets can cover larger distances when carried by air currents.

Once suspended in the air microorganisms reach the host directly when the host inhales aerosolized droplets containing bacteria or viruses. This is how we are infected by many of the respiratory viruses, Legionella pneumophila and Mycobacterium tuberculosis. The other route is indirectly by sedimentation of microorganisms from the air onto surfaces and instruments. The microorganisms are then transmitted by contact with these surfaces or instruments. In case of an endoscopy room this could be a biopsy forceps, the endoscope itself or other instruments.

The number of microorganisms present in the air of a room depends on the quality of the air that is supplied to the room, the number of people present in the room, and the type of activities going on in that room. In an air conditioned room the supplied air has passed through several filters that arrest dust but not bacteria or viruses. However, because bacteria and viruses need a vehicle the supplied air will be relatively clean. People present in the room are a major source of bacteria in the air, most of which are harmless skin bacteria such as Staphylococcus epidermidis. Vavricka et al. [5] showed that during the course of the day, the number of Gram positive bacteria in the air in the endoscopy room increases and that this increase is much less when the colon biopsy forceps is removed with air suctioning than when it is removed without. This is an example of how activities going on in a room influence the number of bacteria in the air in that room.

To assess the risk of transmission of aerosolized microorganisms from the gut during colonoscopy we should consider the seriousness (harmfulness) of the event and the chance that the event occurs. To assess the seriousness, we can examine which microorganisms could be brought into the air during removal of the biopsy forceps and what harm these microorganisms could do. The colon contains millions of anaerobic bacteria. The most harmful and dangerous of these anaerobes with regard to transmission is probably Clostridium difficile, which can cause pseudomembranous colitis. Spores of this bacterium survive very well in the environment for a long time. Nobody would like to have his endoscopy room contaminated with spores of C. difficile. The colon contains numerous aerobic Gram negative bacteria. Escherichia coli is present in almost everyone, but other Gram negatives such as Klebsiella spp., Enterobacter spp., and Pseudomonas aeruginosa are frequently found, particularly in hospitalized patients. Most of these microorganisms, Acinetobacter spp. being the exception, do not survive for long periods in the environment, but long enough to infect the next patient when instruments have become contaminated. These microorganisms may not pose a very serious threat during colonoscopy as long as they are not (multi)resistant. However, (multi)resistance is a growing problem among these Gram negative aerobic bacteria.

Vavricka et al. [5] investigated Gram positive bacteria only. They found predominantly enterococci in their samples, a microorganism that is a common inhabitant of the human gut. As long as these enterococci are fully susceptible to antibiotics their importance is limited. The situation is different however when vancomycin-resistant enterococci provided with virulence factors that promote their spread in hospitals, are transmitted. Of special concern is the transmission of gastrointestinal pathogens such as Salmonella spp. and norovirus. A patient with overt infection generally will not undergo colonoscopy anyway, but Salmonella spp. and norovirus, as with many gastrointestinal pathogens, can be present in the gastrointestinal tract for weeks or even years after the infection. These gastrointestinal pathogens pose a risk not only for patients but also for healthcare workers.

In conclusion, some of the microorganisms that could be brought into the air during removal of a colonoscopy biopsy forceps can do harm. However, there is no proof by hard data that air is a relevant route of transmission in the endoscopy room unlike badly cleaned and disinfected endoscopes, which have been shown to be. So, the chance that transmission occurs cannot be assessed at this time. However, given that air suctioning during removal of a biopsy forceps is easy to perform without any risk to the patient, why should we wait for more evidence before we implement this measure?

Competing interests: None

References

• 1 Lister J. On the antiseptic principle in the practice of surgery.  BMJ. 1867;  2 246-248
• 2 Pasteur L. On the organized bodies which exist in the atmosphere; examination of the doctrine of spontaneous generation.  Annales des Sciences naturelles. 1861;  16 5-98
• 3 Lister J. On a new method of treating compound fracture, abscess, etc. With observations on the conditions of suppuration.  Lancet. 1867;  1 326-329, 357 – 359, 387 – 389, 507 – 509
• 4 Lister J. On a new method of treating compound fracture, abscess, etc.  Lancet. 1867;  2 95-96
• 5 Vavricka S R, Tutuian R, Imhof A. et al . Air suctioning during colon biopsy forceps removal reduces bacterial air contamination in the endoscopy suite.  Endoscopy. 2010;  42 736-741