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. 2023 Sep 1;23(1):323.
doi: 10.1186/s12890-023-02611-4.

A systematic review of the clinical impact of small colony variants in patients with cystic fibrosis

Harrigan Ryan  1 , Emma Ballard  2 , Rebecca E Stockwell  1   3 , Christine Duplancic  1 , Rachel M Thomson  4 , Kimberley Smith  1 , Scott C Bell  5   6   7
Affiliations

A systematic review of the clinical impact of small colony variants in patients with cystic fibrosis

Harrigan Ryan et al. BMC Pulm Med. .

Abstract

Background: Cystic fibrosis (CF) is a life-limiting disorder that is characterised by respiratory tract inflammation that is mediated by a range of microbial pathogens. Small colony variants (SCVs) of common respiratory pathogens are being increasingly recognised in CF. The aim of this systematic review is to investigate the prevalence of SCVs, clinical characteristics and health outcomes for patients with CF, and laboratory diagnostic features of SCVs compared to non-small colony variants (NCVs) for a range of Gram-positive and Gram-negative respiratory pathogens.

Methods: A literature search was conducted (PubMed, Web of Science, Embase and Scopus) in April 2020 to identify articles of interest. Data pertaining to demographic characteristics of participants, diagnostic criteria of SCVs, SCV prevalence and impact on lung function were extracted from included studies for analysis.

Results: Twenty-five of 673 studies were included in the systematic review. Individuals infected with SCVs of Staphylococcus aureus (S. aureus) were more likely to have had prior use of the broad-spectrum antibiotic trimethoprim sulfamethoxazole (p < 0.001), and the prevalence of SCVs in patients infected with S. aureus was estimated to be 19.3% (95% CI: 13.5% to 25.9%). Additionally, patients infected with SCVs of Gram-negative and Gram-positive pathogens were identified to have a lower forced expiratory volume in one second percentage predicted (-16.8, 95% CI: -23.2 to -10.4) than those infected by NCVs. Gram-positive SCVs were commonly described as small and non-haemolytic, grown on Mannitol salt or blood agar for 24 h at 35°C and confirmed using tube coagulase testing.

Conclusion: The findings of this systematic review demonstrate that SCVs of S. aureus have a high prevalence in the CF community, and that the occurrence of SCVs in Gram-positive and Gram-negative pathogens is linked to poorer respiratory function. Further investigation is necessary to determine the effect of infection by SCVs on the CF population.

Keywords: Clinical impact; Cystic fibrosis; Prevalence; Small colony variants.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Fig. 1
Fig. 1
Forest plot of the reported prevalence of Gram-positive (S. aureus) SCVs in included studies (n = 16) utilising a random effects model with the DerSimonian and Laird method. Diamond represents the estimated prevalence of SCVs. ES, Estimate Size
Fig. 2
Fig. 2
Forest plot of the reported mean difference in FEV1% between SCV and NCV patients in included studies (n = 6) utilising a random effects model with the DerSimonian and Laird method. Diamond represents weighted mean difference between SCV and NCV patients. Estimates by Gram status and overall are given
See this image and copyright information in PMC

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