By Carol A. Kemper, MD, FACP

June 1, 2013
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By Carol A. Kemper, MD, FACP, Section Editor: Updates, Clinical Associate Professor of Medicine, Stanford University, Division of Infectious Diseases; Santa Clara Valley Medical Center, is Associate Editor for Infectious Disease Alert.

Risk of TB in older persons

Hochberg NS, et al. Prevention of tuberculosis in older adults in the United States: Obstacles and opportunities. CID 2013;(56):1240-1247.

While the absolute number of cases of tuberculosis (TB) in the United States have declined over the last decade, the risk for reactivation TB in the elderly remains disproportionately high. Some of this risk is the result of an aging immigrant population, longer life-span, and the higher prevalence of co-morbidities in older adults (i.e., diabetes, chronic kidney disease). Older adults (> 65 years of age) living in long-term care facilities have the highest rates of TB in the U.S. (39.2 cases/100,000 persons) – more than 400% greater than that for all age groups. Between 1993 and 2008, 9% of all patients diagnosed with TB in the U.S. resided in a long-term care facility.

These authors examined rates and risk factors for TB in older adults in the U.S. From 1993-2008, 61,124 adults > 65 yrs of age were diagnosed with TB (21.9% of all TB cases in the U.S.). The average yearly rate for persons > 65 yrs or older was 10.9 cases /100,000 compared with 7.3 cases/100,000 for persons aged 21-64 yrs of age – but for persons 85 yrs of age or older, the rate nearly doubled that of the general population (14.2 cases/100,000). Not only did rates of TB increase with advancing age, but in the older population, rates were significantly higher in men, Asian Americans (where the rate was 94.6 cases/100,000 cases), American Indians/Alaska Natives, and in residents of long term care facilities.

From 1998 to 2008, 21% of older persons (including 42% of older patients residing in skilled nursing facilities died while receiving treatment for tuberculosis compared with 7% of younger persons.

The prevention of TB in older patients before they get too much older is therefore especially important. While I believe there generally needs to be a bigger push in this country for chemoprophylaxis of all persons with latent TB, older people — especially those born in countries with endemic TB — should be routinely screened and treated for latent TB as soon as feasible. Though waning immunity in older people may lead to falsely negative PPD/TSTs, limited data suggests that the interferon-gamma release assays may be less affected by age than PPD/TST results, and most older persons are able to mount an adequate immune response for Tb Quantiferon testing.

Non-cocci cocci

Brillhante RS, et al. Coccidioidomycosis in armadillo hunters from the state of Ceara, Brazil. Mem Inst Oswaldo Cruz 2012;(107):813-815.

Infection with Coccidioides posadasii, another endemic pathogenic soil fungi found in certain areas of Texas, Mexico and South America, may provide an alternate explanation for patients at risk for pneumonia not responding to antibacterials. C. posadasii is far less common, and certainly less recognized than its cousin C. immitis, but may result in a similar illness — both in animals and in humans. While it generally causes a self-limited flu-like illness, with fever, sweats, fatigue, cough and chest discomfort, it can result in severe progressive pulmonary and extra-pulmonary disease, with potential dissemination to bones and joints, brain and skin, similar to C. immitis. The recent report above documents an outbreak of infection due to C. posadasii in Armadillo hunters in Northeastern Brazil — the diagnosis of which was delayed while patients received antibacterial therapy.

C. posadasii and C. immitis appear morphologically the same, but are genetically distinct species (first recognized in 2002). C. posadasii also has a much larger range, and is found outside the San Joaquin Valley and areas recognized as “cocci country” — including the semi arid areas of Texas, the southern desert of Mexico, and parts of South America. It is quite hardy, much more draught tolerant than its cousin, and tolerates soils with high salinity and highly variable pH. So if you are seeing what looks like a cocci case without the appropriate epidemiology — you might be correct. Cultures of clinical material still represent a biohazard for laboratory workers — but real time PCR assays used for the detection of C. immitis in clinical specimens do not distinguish between the two species.

A new “App” for your mobile phone

Bogosh II, et al. Short Report: Mobile phone microscopy for the diagnosis of soil-transmitted helminth infections: A proof of concept study. Am J Trop Med Hyg 2103;88:626-629.

Nowadays, mobile phones can go almost anywhere in the world — and compared to bulky cameras and light microscopes, are cheap and easy to carry. These authors conducted a proof of concept study to assess whether a mobile phone could be modified to detect intestinal parasites in stool.

Stool samples were collected from school aged children in Tanzania over a 5-day period, and were processed using the Kato-Katz technique. The thick smears were evaluated by a trained technician using conventional light microscopy, with the number of Ascaris and Trichuris spp. eggs and the number of hookworms tabulated, and compared with the results obtained using a mobile phone “microscope.”

A mobile phone was transformed into a microscope using a 3 mm ball lens and a piece of double-sided tape. A small aperture was created in the tape, into which the lens was inserted; and two extra little bits of tape were placed on either side of the lens — in order to give some “depth” to the field, and creating a 1 mm space between the slide and the lens. The phone was placed over the stool slide, and illuminated by a hand-held flashlight (using a AA battery). The authors estimate the whole contraption took about 5 minutes to assemble and cost $15. While the estimated magnification was about 50-60 x, the resolution was not as good as hoped — apparently the smaller 1 mm lens had better resolution but a narrower field of view, so they had opted for the 3 mm lens, hoping it was adequate.

A total of 199 thick smears were compared. For any helminth, the sensitivity of the mobile phone microscope, compared with the conventional light microscopy results, was 69%. The best results obtained using the mobile phone were observed for A. lumbricoides eggs (81%) followed by T. trichuria eggs (79%); the worst result was observed for the detection of hookworms (14%), possibly because hookworms quickly clear on smears. Heavy eggs burdens were easier to detect (93% sensitivity).

Since the resolution with the mobile phone microscope was not as good as hoped with the 3 mm lens, several false-positives were observed, leading to a lower specificity (61%). The authors believe, however, their low-tech approach was nearly adequate, and could likely be improved upon with a better lens – yielding an inexpensive, small portable tool for use in developing countries with limited laboratory access and resources. Since one simple approach in such countries is “see an egg, treat an egg”, accuracy may not be paramount, as detection of any egg in stool could be used as a basis for broader anti-helminthic treatment.