Small colony variants (SCVs) of Staphylococcus aureus have a high prevalence in patients with cystic fibrosis (CF) and are associated with previous use of trimethoprim sulfamethoxazole (SXT), according to study findings published in BMC Pulmonary Medicine.

Researchers conducted a systematic review to evaluate the prevalence of SCVs of common respiratory pathogens, clinical characteristics associated with their occurrence, and laboratory phenotypic features to support laboratory diagnosis in patients with CF.

The researchers searched for studies involving patients with CF that reported on respiratory pathogens including SCVs and clinical outcomes of patients with SCVs vs patients not infected by SCVs. Conducted in April 2020, the search included studies published in English in the PubMed, Web of Science, Embase, and Scopus databases. The studies were classified according to whether they evaluated Gram-positive or Gram-negative pathogens.

The review included 25 full-text articles. The 21 Gram-positive studies focused on S aureus, and the 5 Gram-negative studies assessed Pseudomonas aeruginosa (n=3), Stenotrophomonas maltophilia (n=1), and Burkholderia cepacia complex (n=1). Additionally, 1 study included Gram-positive and Gram-negative pathogens.

Bacterial infection in CF plays a large role in adverse health outcomes, and the further study of SCVs and how they bring about these adverse outcomes will be necessary to better the treatment and management of CF in future.

The analysis of previous antibiotic use included 6 studies, and all reported on SCVs of S aureus in patients with SCV and non-small colony variants (NCV). Among these studies, 2 evaluated antibiotic use in the preceding 36 months, 2 in the previous 12 months, 1 for the preceding 6 months, and 1 for ongoing antibiotic use. Previous use of SXT was more common in patients with SCV (68.2%) vs NCV (28.5%) (P <.001).

S aureus had an SCV prevalence rate of 19.3% (95% CI, 13.5%-25.9%) in a meta-analysis of 16 (64.0%) studies. Gram-negative pathogens were excluded from analysis because of the small number of studies and range of pathogens assessed.

The meta-analysis comparing lung function of patients in the SCV and NCV cohorts included 5 studies and showed that forced expiratory volume in 1 second percent predicted (FEV1%) was 16.8% lower (95% CI, -23.2 to -10.4) in patients infected with SCVs vs those infected with NCVs.

Respiratory sputum samples were the most frequently acquired sample types taken from patients with both Gram-positive and Gram-negative pathogens (17/18 [94.4%] and 2/3 [66.7%] of valid studies, respectively). Gram-positive species were commonly confirmed with use of tube coagulase testing (11/18 [61.1%]), agglutination testing (10/18 [55.6%]) and polymerase chain reaction amplification of the nucA gene (8/18 [44.4%]).

Limitations include use of only English-language studies and the limited number of Gram-negative and FEV1% studies. In addition, the analysis of diagnostic methods used only descriptive frequencies of the reported methods, and the findings were primarily based on studies with SCVs of S aureus.

“Bacterial infection in CF plays a large role in adverse health outcomes, and the further study of SCVs and how they bring about these adverse outcomes will be necessary to better the treatment and management of CF in future,” stated the study authors.

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