Antibody testing for Mycobacterium avium complex infection in cystic fibrosis patients

Abstract

Background: Mycobacterium avium complex (MAC) is recognized as a severe pathogen among patients with cystic fibrosis (CF). Early signs of pulmonary disease with MAC can be missed in patients with CF due delays in mycobacterial culture results. A common problem is inconclusive results due to lack of representative material from the lower airways. The objective of this study was to test the diagnostic accuracy of a method for investigating IgG-activity against MAC. Materials/methods: Clinical data from 309 CF patients from the Copenhagen CF Center combined with collected serum samples for antibody determination by ELISA were used for a cross sectional analysis. CF patient cases were retrospectively identified and assigned one of four defined groups based on their mycobacteria culture results up to and including 2015. Mycobacterial antigen preparation was performed using a MAC serovar obtained from a MAC-infected patient. Anti-MAC IgG levels were measured from serum samples and expressed in ELISA units. The test positivity threshold for MAC cases was determined using a receiver operation curve. A longitudinal analysis of antibody kinetics before and after culture conversion was performed in MAC positive patients between 1984-2015. Results: Results showed that anti-MAC antibody levels were significantly correlated to whether patients fulfil established criteria for MAC pulmonary disease (Figure 1). Longitudinal kinetics showed rising antibodies prior to first positive culture suggesting a diagnostic delay relying only on cultures. Conclusions: Routine antibody screening for MAC can stratify patients according to risk for MAC pulmonary disease, helping clinicians decide how to prioritize.