TB Infection Control

Yes, the public health response to flu is different that TB because, as
best we know, unlike TB, flu appears to spread both by airborne droplets
and large droplets - an extension of direct contact. There are famous
cases of airborne spread, on an airplane for example, but spread by
direct contact from large respiratory droplets appears to predominate -
although the exact percentages are difficult to estimate. TB is an
infection of the alveolar macrophage, generally requiring 1-5 micron
particles (ie airborne particles) to avoid impaction higher up the
respiratory tract, which is relatively immune. Moreover, there is
evidence that a single virulent Mtb organisms can cause TB in a
susceptible host. Influenza appears to infect respiratory mucosa higher
up, possibly nasal, oral, and possibly ocular mucous membranes. How
large a dose (innoculum) is needed probably varies with the virulence of
the strain, but much larger inoculums are transferred by large droplets
or direct contact compared to droplet nuclei spread.

The surgical masks that are being used may reduce inhaled particles by
50% or so, which is not insignificant, but their main purpose in my view
is to reduce the probability of hand to mouth or hand to nose transfer
by ...

Yes, the public health response to flu is different that TB because, as
best we know, unlike TB, flu appears to spread both by airborne droplets
and large droplets - an extension of direct contact. There are famous
cases of airborne spread, on an airplane for example, but spread by
direct contact from large respiratory droplets appears to predominate -
although the exact percentages are difficult to estimate. TB is an
infection of the alveolar macrophage, generally requiring 1-5 micron
particles (ie airborne particles) to avoid impaction higher up the
respiratory tract, which is relatively immune. Moreover, there is
evidence that a single virulent Mtb organisms can cause TB in a
susceptible host. Influenza appears to infect respiratory mucosa higher
up, possibly nasal, oral, and possibly ocular mucous membranes. How
large a dose (innoculum) is needed probably varies with the virulence of
the strain, but much larger inoculums are transferred by large droplets
or direct contact compared to droplet nuclei spread.

The surgical masks that are being used may reduce inhaled particles by
50% or so, which is not insignificant, but their main purpose in my view
is to reduce the probability of hand to mouth or hand to nose transfer
by direct contamination of the hands. As you know, the main advice being
given is hand hygiene, a practice that has no benefit for TB
transmission.

I hope this clarifies the differences between flu and TB transmission.

Ed

Edward A. Nardell, M.D.
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
Divisions of Global Health Equity and Pulmonary Medicine
FXB Building, 709c
651 Huntington Ave.
Boston, MA 02115

Dear Ed,

Thank you very much for your comprehensive and valuable response.

Ridha
Dr Ridha Djebeniani
STB Medical Officer, WHO Djibouti.

I don't know if this is appropriate but from the 21-23rd Sept we are holding the First African IPC Congress in Kampala, Uganda- one of the main themes of a few sessions will be the TB-IPC standing in Africa and what one can do to improve it. We would like participation from Africa so that one can come forward with decisions regarding the use of appropriate protective clothing in airborne and droplet infections.
The website is http://www.ipcan2009.co.za if anyone is interested in attending- the WHO and other large organisations working with IPC will be present.
Or you can contact me.
Thanks
Shaheen


Prof Shaheen MehMBBS, FRC Path (UK), FCPath (Micro) (SA), MD (Eng)
Head of Academic Unit for Infection Prevention and Control
Tygerberg Hospital & Stellenbosch Uni
PO Box 19063,
Tygerberg 7505, Cape Town

FYI: the Institute of Medicine (IOM), U.S. just released an online guide: “Pandemic Influenza: A Guide to Recent Institute of Medicine Studies and Workshops” available here: http://www.iom.edu/?id=66154. It provides PDF downloads and recaps to all major IOM publications related to policy issues for pandemic influenza and other infectious disease threats similar to the current spread of H1N1 (SO) influenza. These include information for the implementation of pandemic planning and response in the following areas: Communicating with and engaging the public; Use of masks and personal protective equipment; Use of antiviral drugs and vaccines; Outbreak mitigation (e.g., social distancing, school closures); Surveillance, research, and evaluation during a pandemic.
The CDC also provides comprehensive up-to-date information at the following link: http://www.cdc.gov/h1n1flu/

Dear Prof. Mehtar,
I believe that this is a good platform to break the news about the upcoming
1st African IPC Congress.
I must say that it is refreshing to know that at long last we now have a
forum to discuss IPC issues in Africa. The rest of the world has gone ahead
of us but we have not necessarily been left behind! We are coming up strong!
Thank you for all the work done in the background to bring this Congress to
fruition! Thank you.
Nii Nortey