Report of the UK Cystic Fibrosis Trust Antibiotic Working Group

although not all authors have found these factors to be relevant. 116-121 [3] NTM are found in therespiratory secretions of up to 20% of patients with CF, if appropriate isolation methods are used. 122[3] A multicentre North American study commenced in 1992 and completed in 1998 has confirmedthe prevalence of NTM, defined as having at least one positive culture, in patients with CF as 13%(128/986) which varied between CF clinics from 7% to 24%. A total of 2.5% of patients (25/986)fulfilled the American Thoracic Society (ATS) criteria at that time of either 2 positive cultures and apositive smear or 3 positive cultures. Mycobacterium avium was cultured most frequently (72%) withMycobacterium abscessus being the next most common (16%). 123 [2+] In this largest study ofprevalence of NTM in CF the patients with positive cultures were older and had relatively mild lungdisease but worse nutritional status. In addition they were more likely to have concomitant S.aureusinfection rather than P.aeruginosa.7.8.2 Clinical significance of non-tuberculous isolates in sputa from patients withcystic fibrosisThe significance of the isolation of non-tuberculous mycobacteria (NTM) from respiratory secretionsremains unclear despite a number of clinical reports. Non-tuberculous mycobacteria areenvironmental organisms that have been recovered in soil, dust and drinking water systems. Therecovery of NTM in sputum of a person with CF poses a diagnostic dilemma. The question arises asto whether the isolate represents transient contamination of the airways, colonisation, or trueinfection. There is no consistent evidence that antibiotic treatment is beneficial. The ATS criteria fordiagnosis of disease have recently been revised. 124 [4] Although not specifically designed for CF, theyare helpful in guiding investigation. Minimum evaluation should include an HRCT scan, three ormore sputum samples for acid fast bacilli analysis and exclusion of other disorders. In the case ofindividuals with CF and suspected NTM infection, it is important to first treat their usual pathogensand then assess whether anti mycobacterial therapy is warranted.The largest study of NTM in the US revealed that FEV1 decline was no different overall in the shortterm in people with or without NTM infection but that all subjects with 3 or more positive culturesshowed evidence of progression of disease on CT scan compared to controls. 125 [2+] Thus a stepwiseapproach to consideration of therapy can be recommended (figure 7.1) with the first requirementbeing ATS microbiological criteria of at least two positive sputum cultures or a single positive lavage.The second step is the HRCT as an abnormal HRCT at baseline in keeping with NTM infection waspredictive of progression in the American cohort. 126 [2+]Furthermore evidence that infection with Mycobacterium abscessus is associated with significant diseaseallows further stratification for treatment. 127–129 [3] We suggest the guide to assessmentrecommended by Olivier et al 130 and suggest that this is validated in future studies. (figure 7.1)Cystic Fibrosis Trust 7.8.2March 2009