(58) The limited clinical value of ongoing microbiological surveillance for children with cystic fibrosis admitted for antibiotic treatment

Background: Often performed for fear of undetected airway pathogens causing inappropriate antimicrobial therapy, airway microbiological surveillance for cystic fibrosis (CF) patients is one practice with little data to justify its use in management of pulmonary exacerbations (PEx). These repeated airway cultures have unknown benefits for treatment with increased healthcare costs and staff time. Further, people with CF with negative airway bacterial cultures still often respond to treatment and there is little change in the microbial composition of sputum cultures despite treatment of broad-spectrum antibiotics [1,2].

At BC Children’s Hospital, standard of care is to obtain airway cultures and antimicrobial susceptibility testing upon admission and weekly thereafter to guide antimicrobial selection. This study aims to describe the frequency with which repeated airway cultures identify new pathogens during a PEx admission and assess whether the results of these cultures impacts clinical management.

Methods: This is a retrospective study of all children with CF with at least one hospital admission for IV antibiotics from January 1, 2015 to December 31, 2019. Deidentified demographic data, culture results, and antibiotic prescription history were collected from electronic medical charts. Airway cultures were numbered starting from the last culture taken in clinic prior to admission (ie. ‘Culture 1’), culture on admission to hospital (‘Culture 2’) and so on (‘Cultures 3-6’). “New bacterial growth” is defined as the presence of a bacterial isolate on one culture not seen on previous culture. Descriptive statistics were applied using R version 4.0.3.

Results: Analysis included 79 patients with 225 admissions. The median duration of admission was 13 (IQR 10, 15) days. Most admissions (160/225; 71%) maintained the initial antibiotic therapy, with 89 antibiotic changes seen over 65 admissions. In most admissions where antibiotics were switched, they were only switched once (47/65; 72%).

Most admissions (209/225, 92.9%) had four or fewer cultures taken. Almost all (218/225; 96.9%) admissions showed changes (gain or loss) in microbiology during hospitalization but only 82 (36.4%) had growth of new pathogens (137 total new pathogens; Table 1). Of all new pathogens identified, 94/137 (68.6%) were found between Cultures 1 and 2 (Table 1). Methicillin sensitive Staphylococcus aureus (37/137, 27.0%), non-Pseudomonas aeruginosa Gram-negative bacilli (37/137, 27.0%) and Pseudomonas aeruginosa (22/137, 16.1%) were the most commonly identified new pathogens. New pathogens were more commonly seen between Cultures 1 and 2 (94/137, 68.6%) than in all cultures thereafter (43/137, 31.4%), and antibiotic changes were more likely after a new organism in Culture 2 (31/94, 32.9%) than in Cultures 3-6 (5/43, 11.6%).

Conclusions: Ongoing bacterial surveillance during a CF PEx provided minimal additional information compared to cultures collected on admission (Culture 2) and later cultures rarely altered clinical management. This suggests there is limited benefit to continued airway microbiological surveillance past the admission culture.

Acknowledgements:

References: [1] Zemanick ET, Wagner BD, Harris JK, et al. Pulmonary exacerbations in cystic fibrosis with negative bacterial cultures. Pediatr Pulmonol. 2010;45(6):569-577.

[2] Fodor AA, Klem ER, Gilpin DF, et al. The Adult Cystic Fibrosis Airway Microbiota Is Stable over Time and Infection Type, and Highly Resilient to Antibiotic Treatment of Exacerbations. PLoS One. 2012;7(9).