Chronic lung infections caused by a variety of bacteria are a serious complication in people with idiopathic pulmonary fibrosis (IPF), and are particularly risky for those with low oxygen pressure in the blood or high levels of the lung disease biomarker KL-6, a study has found.
The researchers recommended greater attention be paid to chronic lung infections in IPF patients, especially those with risk factors identified at diagnosis.
The study, “Incidence and etiology of chronic pulmonary infections in patients with idiopathic pulmonary fibrosis,” was published in the journal PLOS ONE.
People with IPF experience a higher rate of lung infections caused by a variety of microorganisms. These infections can be short-term (acute) such as lower respiratory tract infections (LRTI) and pneumonia. But they also can be persistent; those are called chronic pulmonary infections (CPIs). CPIs include tuberculosis, nontuberculous mycobacteriosis (NTM), chronic pulmonary aspergillosis, and nocardiosis.
Despite this understanding, the rate of new CPI cases (incidence), along with their causes (etiology) and risk factors, has not been adequately investigated in people with IPF.
To fill this knowledge gap, researchers at the Saitama Cardiovascular and Respiratory Center in Japan analyzed the medical records of 659 people with IPF treated at the institute from January 1995 to July 2010.
For the analysis, the team defined a CPI as a chronic infection with known cause diagnosed at least one month after IPF diagnosis, or the appearance of shadows on chest X-rays or computed tomography (CT) scans.
The assessment was done by dividing patients into four groups according to whether or not they had CPIs at diagnosis, and if they developed a CPI during follow-up (or not). The median follow-up time was 6.1 years.
Of the patient records analyzed, 557 were CPI negative at IPF diagnosis and did not develop CPI in the follow-up period; 46 patients were CPI negative but developed a chronic infection during follow-up. Twenty-eight patients were CPI positive at IPF diagnosis, but did not acquire another infection during follow-up, while the remaining eight patients were CPI positive and went on to develop a different infection.
The analysis showed that the number of new cases of CPIs in people with IPF was 18.9 cases per 1,000 person-years (the gathered follow-up years of all included patients in a specific study). As the rate of acute pneumonia in IPF patients was determined previously to be 45.6 cases per 1,000 patient-years, the researchers recommended that “clinicians should pay attention to CPI development during follow-up.”
The microorganisms detected at diagnosis were M. tuberculosis in 16 patients, M. avium complex (MAC) in 12, five patients had Aspergillus, and Nocardia (causing nocardiosis) was found in two patients. In those who developed CPIs during follow-up, 17 patients had M. avium complex, 16 had Aspergillus, and M. tuberculosis was detected in six patients.
An infection with NTM had the highest incidence, with 9.71 cases per 1,000 person-years, followed by chronic pulmonary aspergillosis with 8.81 cases per 1,000 person-years, M. avium complex (MAC) lung disease with an incidence of 8.04, and tuberculosis with 2.76 cases per 1,000 person-years. Overall, of the 82 patients with a CPI, 17 of the infections were caused by a mix of bacteria.
A statistical calculation found two risk factors for CPI development in IPF patients: low oxygen pressure in the blood (PaO2), measuring less than 70 Torr (normal range is 80 to 100 Torr), and a high level of the lung disease biomarker known as KL-6 (more than 2,000 U/mL).
An assessment of the mortality rate found, however, no differences in mortality between those with CPI compared to those without CPI.
“In conclusion, the present study showed that CPI was an important complication in patients with IPF,” the researchers wrote. “Nontuberculous mycobacteria, M. tuberculosis, and Aspergillus and Nocardia species were the four most frequent etiologies of CPI in patients with IPF.”
Because a low PaO2 and high KL-6 levels “were found to be risk factors for CPI development, greater attention should be paid to IPF patients with these risk factors during follow-up,” they recommended.
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