Time-to-first-isolation of methicillin-resistant Staphylococcus aureus (MRSA) in cystic fibrosis (CF): An underutilised metric in infection control?

Background: Methicillin-resistant Staphylococcus aureus (MRSA) has emerged as a significant pathogen in people with cystic fibrosis (PwCF). There is a paucity of reports on MRSA infection dynamics within CF. It was the aim to examine the utility of Time-To-FirstIsolation (TTFI) metric and to correlate this with patient gender and CF transmembrane conductance regulator (CFTR) mutation type.

Methods: The microbiology of respiratory specimens from 100 adult (≥18 years) PwCF was examined (50 females; 50 males; mean age 24.6 years ±6.25 (SD)) from birth to present, equating to 2455 patient years. TTFI was determined in relation to (i) presence/absence of MRSA, (ii) CFTR mutation type and (iii) PwCF gender.

Results: MRSA was noted in 23% patients (10 female/13 males); (i) F508del/F508del homozygous (43.5%) and (ii) F508del/other heterozygous (56.5%). No non-F508del CFTR mutations types were noted. The median and mean TTFI was 137 months and 127.4 months respectively, shortest time was 23 months, longest time 211 months. There was no statistical significance in TTFI in relation to CFTR mutation group (p = 0.39) or gender (p = 0.71).

Conclusions: TTFI is useful and applicable to the chronic infection model, where patients with a specific underlying disease are predisposed to acquire infections and where these infections are likely to become chronic. Intelligence offered by TTFI provides a window of opportunity to target IPC interventions, to help prevent MRSA acquisition. CF multidisciplinary teams, microbiologists and infection prevention specialists should utilise such TTFI data from their respective centres to help inform and plan intervention strategies to help prevent MRSA acquisition.