Rats!!! I think you have Tuberculosis

Gambian pouched rat before ID rounds

We recently reported that the WHO endorsed the use of Cepheid's rapid TB test that carries a $17,000 fixed device cost and $17/test cost in developing countries.  The device would cost $64,000 in the US.  In yesterday's NY Times there was an article discussing a recent report in The American Journal of Tropical Medicine and Hygiene by Alan Poling at Western Michigan University that found that the Gambian pouched rat was far better than standard microbiological tests for TB diagnosis. In 10,523 patient, the rats trained to smell the sputum samples found 44% more cases. Sensitivity was reported as 86.6% and specificity was 93%.

Wow.  I hope these results can be validated in other settings.  If these rats are equally or more accurate than standard or rapid TB tests with minimal costs, there is no reason why they would have to be limited to resource-poor settings, right? Compared to a $64k rapid test plus test costs, I bet the rats would be very cost-effective; especially if they are more effective. It would be pretty cool to see ID clinicians carrying 15 pound rats around with them on rounds. 

Poling A. et al AJTMH, December 2010
NY Times article, January 3, 2010

WHO backs rapid test for TB - If only we had rapid treatment

I heard on NPR this morning that the WHO (Keith Moon died 32 years ago) is supporting the new rapid TB test made by Cepheid (MTB/RIF test).  You can read more about the test characteristics in the recent NEJM article. They reported 98% sensitivity in smear-positive patients but only 73% sensitivity in smear-negative patients after a single test.  Sensitivity rises to 85% after a second test and to 90% after a third test.  The test was very good at identifying rifampin-resistant and rifampin-sensitive strains (both around 98% of the time).

The NPR article states that the processor costs $64,000 in US but could be $17,000 for developing countries.  Tests will cost $17.  If you need to do three tests in smear-negative patients to rule out TB with a sensitivity of 90%, it would cost $51. I wonder if developing country budgets can absorb that cost?

Don't wait in a doctor's waiting room

I should have said don't wait too long in the "waiting area of healthcare premises" especially if another occupant/patient has measles, as the authors of a new study in BMC Infectious Diseases report.  The authors analyzed the likelihood of acquiring TB, influenza or measles during stays of 30 or 60 minutes in a standard waiting room using a mathematical model simulation.  One caveat is that they assumed one person in the waiting room was infectious with one of the organisms. Thus, while the results provide nice theoretical estimates of airborne transmission for these highly (measles), moderately (influenza) and minimally (TB) infectious organisms, they don't adjust for the probability of an occupant having the infection in the first place (influenza>TB>measles).   

With that important caveat, the likelihood of acquiring TB during a 30 minute stay in a waiting room was 0.3% and was 0.8% for a 60 minute stay.  For influenza, the numbers were 2.6% and 6.6% at 30 and 60 minutes and were 13% and 31% for measles.  With those numbers, if there is measles in the community at all, it's probably best to avoid any waiting area (unless you've been vaccinated). Nothing surprising in the results, really, but still worth quantifying and thinking about.  During the H1N1 season last year, I was always worried about transmission in the various hospital waiting areas.  In those situations, it was likely that >1 person had infectious influenza in the waiting room.  I hope future studies analyze the impact of # of infectious occupants and likelihood of those infectious occupants being present during various seasons (RSV, Influenza etc).

Once last thought.  Next time a clinician keeps you waiting, you might mention that he/she has put you at increased risk for getting sick.


Beggs et al. BMC ID article

Sunday reading

A couple recent New York Times articles relevant to infection prevention are worth a read. The first reports on an Annals of Internal Medicine paper describing how cost and reimbursement serve as barriers to the uptake of the adult varicella zoster virus (VZV, shingles) vaccine. The second is a fascinating story about the last of the old-time TB sanitariums. Although directly observed therapy (DOT) outside the hospital is the current model, there are some for whom prolonged inpatient care is needed, including those with dual diagnoses or extremely-drug resistant TB for whom simple outpatient DOT regimens are not feasible.

NY Times article on VZV vaccine
Annals paper describing barriers to vaccine uptake
NT Times article on A.G. Holley TB hospital