An antibody test might be a better way to diagnose chronic Pseudomonas aeruginosa lung infection among patients with bronchiectasis than the currently used sputum sampling, researchers from Britain and Spain recently showed.
A study titled “Anti-Pseudomonas aeruginosa IgG antibodies and chronic airway infection in bronchiectasis,” which examined more than 400 patients, also suggested that the test might be a marker for disease severity and response to antibiotic treatment. The work was published in the journal Respiratory Medicine.
While Pseudomonas infection in patients with bronchiectasis is common and linked to poor outcomes, diagnosing a persistent infection is not always straightforward.
Diagnosis is made using repeat sputum samples, but in contrast to some other diseases in which Pseudomonas is common, sputum sampling is not done on a routine basis in bronchiectasis patients in Europe — preventing the diagnosis of chronic infection in these patients.
The team recruited 408 bronchiectasis patients, of which 14.7 percent had been diagnosed with chronic Pseudomonas infection before the study. All patients had a blood sample taken at the start of the study.
Those previously diagnosed with chronic infection had higher levels of anti-Pseudomonas antibodies. Researchers defined a positive result as more than 2.96 units. Such a result was found in 95 percent of patients diagnosed with chronic infection with the help of sputum samples. In addition, 25.6 percent without a diagnosis had antibody levels higher than the cutoff value.
Among the 89 patients who tested positive without having a previous diagnosis, 37.1 percent had a chronic infection with another bacterium — Haemophilus influenzae. This infection was present in 31.1 percent of all patients in the study. When researchers removed these individuals from the analysis, the ability of the test to correctly identify people without a Pseudomonas infection increased.
An additional 11.2 percent of people who tested positive without a previous diagnosis had a positive sputum test for Pseudomonas, but had not met the criteria for chronic infection — having two or more positive sputum tests three months apart. Six of these 10 people later had another positive sputum sample, suggesting the test correctly identified them as positive for Pseudomonas infection.
When researchers used stricter criteria for chronic Pseudomonas infection, the antibody test correctly identified all affected patients.
In addition, the test seemed valuable also in predicting disease severity. Pseudomonas antibody levels were found to be related to the number of earlier exacerbations, disease severity scores, and the number of immune cells in sputum. The test also correctly identified a large proportion of patients who got rid of their infection after treatment.