Viability of TB organisms in air. By Edward Nardell, MD Moderator | 20 Oct, 2010 Last edited by Sophie Beauvais on 01 Dec 2010

Dear colleagues,

I was recently asked the following by a colleague at MSF France:

- how long time can a droplet nuclei remained suspended in "regular/lab conditions" and what's the level of impact of certain measures on it (like humidity) ?

- I've found that the survival of mtb outside the host is: Sputum (cool and dark location) : 6 to 8 months, clothing : 45 days, paper - book : 105 days (this is the reference: and m bovis its viability (half life) is around 1.5 hours after airborne
but no info on airborne mtb. Any info on this?

I replied:

There are only two papers on the viability of mycobacteria in air, both done in rotating drums with controlled humidity, etc., and they had very different results. One is old, done in the 60s by Loudon (Loudon RG, et al, Am Rev Resp Dis 1969; 100:165-171) and showed a half life for M. tuberculosis of about 6 hours. More recently, workers in the UK repeated the study with aerosolized organisms from actively replicating organisms from continuously fed cultures. They found at T 1/2 of about 20 mins. (Leve, et al, Letters in Appl Microbiol 2000; 31:238-241). We will try to post these references on GHDonline.

I tended to believe the 6 hr figure as the upper limit. Humidity was 50% I believe in the Loudon study, but 75% in the Lever study. Our own UV studies suggest that high humidity was protective for the organism against UV damage - possibly other insults as well. For respiratory viruses, however, high humidity is deleterious, so you cannot be sure. However, these studies are all artificially generated aerosols and human generated aerosols could be quite different.

Recent studies have shown that many organisms in the airways retreat to a spore-like inactive state that would likely favor survival. Most importantly, ventilation determines the presence of viable tubercle bacilli in air much more than viability. In a room with just 1 air change per hour, 63% of organisms are gone in an hour, 84% in two hours, and over 90% in 3 hrs. With 6 ACH, of course, organisms are gone in minutes. As you know, viability of organisms on surfaces is inconsequential since they must be inhaled to infect humans.

I hope this helps.

Edward A. Nardell, MD



S. Mehtar Replied at 12:55 PM, 20 Oct 2010

Dear Ed
This information is very useful to us in countries where there is little ventilation in clinical areas. It is indeed very helpful.
I have another question which I hope the group can help me with.
Do we know how much spread can be contained by the person who is infected wearing a face mask? In other words can we reduce the number of bacilli by covering our mouth when coughing. And if so, by how much?
I can't find any literature on this.

Prof Shaheen Mehtar
MBBS, FRC Path (UK), FCPath (Micro) (SA), MD (Eng)
Chair IPC Africa Network
Head of Academic Unit for Infection Prevention and Control
Tygerberg Hospital & Stellenbosch Uni
PO Box 19063,
Tygerberg 7505, Cape Town
Visit the First African IPC Congress website

Shelly Batra, MD Replied at 1:05 PM, 20 Oct 2010

Thank you Dr. Nardell, this is very insightful information with immense practical applications.
Also I have a question. Is there any study on the effect of sunlight ( or UV rays) on Mycobacteria? if not, I would appreciate your views on the subject
Shelly Batra, MD
President, Operation ASHA
Fighting Tuberculosis Worldwide

Edward Nardell, MD Moderator Replied at 6:20 PM, 20 Oct 2010

Hi Shelly,

The effects of germicidal UV on airborne TB is now well established by experimental chamber studies and finally by two studies in hospitals using real TB patients and guinea pig sentinel air sampling (Escombe, published in PLoS, our study in preparation). The later studies employing upper room UV fixtures showed 70 and 80% efficacy, respectively.

Sunlight contains UV, but it is exclusively UV A and UV B (longer wavelength UV) compared to the shorter wavelength UV C which is emitted from UV lamps used for air disinfection. While I am sure it will have some germicidal effect, UV C is much closer to the action potential (effective absorption wavelength) for killing bacteria than is UV B, and much, much closer than UVA. There is no UV C in sunlight. Moreover, UVB, and less so UVA, is absorbed by window glass, further reducing the UV in sunlight indoors through glass. Outdoors, dilution rather than UV is probably the more important protection factor. However, it is hard to imagine airborne organisms outside surviving long in direct sunlight. I don't have any papers testing sunlight against TB, but I believe it has been done.


Edward A. Nardell, MD
Associate Professor
Harvard Medical School (Medicine; Global Health and Social Medicine)
Harvard School of Public Health (Environmental Health; Immunology and Infectious Diseases)

Brigham and Women's Hospital
Division of Global Health Equity
FXB Building, 709c
651 Huntington Ave.
Boston, MA 02115

Sandeep Ahuja Replied at 6:26 PM, 20 Oct 2010

Thanks Ed. You are a storehouse of knowledge.
Sent from my BlackBerry® on Reliance Mobile, India's No. 1 Network. Go for it!

Gabit Ismailov Replied at 4:19 AM, 21 Oct 2010

Dear Dr Nardell,

There is a rather old but informative publication by Dr John Weinzirl [1] studying the action of sunlight on MTB. In his experiments MTB was killed in 2-10 min by direct sunlight when planted upon glass or paper.

Kind regards,

Dr Gabit Ismailov
Medical Officer
Tuberculosis Control Programme

[1] Weinzirl, J. (1906). "The Action of Sunlight upon Bacteria with Special Reference to B. tuberculosis." Public Health Pap Rep 32(Pt 2): 128-153.

Shelly Batra, MD Replied at 10:48 AM, 21 Oct 2010

Dear Dr. Ismailov

This is very interesting. NGOs working at grassroot level usually do not have the resources to carry out any such experiments. So this community has proved a great resource. We just rely on the sun and wind for killing/dispersing bacteria !
Shelly Batra, MD
President, Operation ASHA
Fighting Tuberculosis Worldwide