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Fungal Infections and Antimicrobial Resistance Rates: Part 2

JAN 22, 2017 | SARAH ANWAR

Chronic Pulmonary Aspergillosis Misdiagnosed as Tuberculosis

According to a 2008 study, patients with smear-negative pulmonary tuberculosis (TB) are often less infectious than those who are smear-positive. Smear-negative cases refer to patients who are diagnosed with TB despite not being infected. The researchers recognize that those who are misdiagnosed with TB may actually have chronic pulmonary aspergillosis (CPA), a condition that mimics the effects of TB. They note that in a study out of the United Kingdom involving 544 patients who had been treated for TB, 134 went on to develop precipitating antibodies to Aspergillus fumigatus within 2 years; within 5 years, 34% of the total patient population had developed precipitating antibodies to Aspergillus fumigatus. Of the 134 patients, 58% (78) went on to develop late stage CPA within 2 years. However, the researchers report that “few prospective studies have been conducted on CPA after treatment for TB, so the incidence of such cases cannot be stated with certainty; conservatively, however, a rate of ≈10% among survivors of pulmonary TB is likely and a global prevalence of ≈1.2 million cases is probable.”
The researchers warn that culture testing smear-negative patients for Myobacterium tuberculosis is slow and may yield false negatives. They recommend testing respiratory specimens through DNA detection assays, although this method is also not 100% accurate. Among smear-negative patients, many have relapsed after receiving treatment for TB, while many of those cured of TB have developed CPA. The researchers also warn that death rates in HIV patients are higher among those with smear-negative pulmonary TB as opposed to those with smear-positive. They state, “It is increasingly recognized that many of these patients are chronically infected with Aspergillus spp., resulting in CPA that is largely undiagnosed and untreated.”
The researchers then go on to state that signs and symptoms as well as chest radiographs are similar in both TB and CPA patients. They also note that CPA is a common complication associated with TB infection, and that the associated life expectancy among CPA patients has a “5-year death rate of 75%-80%.” Thus, it is recommended to actively test for CPA in patients who already completed antimicrobial therapies for TB but are still presenting with symptoms.

To properly diagnose CPA infection, the researchers recommend using Aspergillus antibody detection, which has 96%-97% sensitivity and 92%-98% specificity. Citing two studies with high rates of fungal infections in patients thought to be infected with TB, the researchers concluded, “This finding and the recognition of patients with pulmonary histoplasmosis or coccidioidomycosis indicate that other, potentially treatable diseases, not smear-negative TB, may be responsible for illness attributed to TB.”
The researchers then go on to state that it is “unnecessary” to empirically treat patients with fungal infections, such as CPA, for TB, citing that it is “ineffective” and harmful. When TB treatment does not seem to show any signs of alleviating infection, physicians frequently believe that the patient has drug-resistant TB, utilizing second- and third-line TB medications, note the researchers. This not only increases the economic burden on patients, it also leads to an increased risk of drug resistance.

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