Epidemiological surveillance and wild-type MIC distribution of Legionella pneumophila in north-western Spain. 2003-2016

Purpose: To perform epidemiological surveillance of Legionella pneumophila in recreational swimming pools in the city of Valladolid (Spain), an area with a continental climate and low incidence of legionella-associated infections. Additionally, wild-type minimum inhibitory concentration (MIC) distributions for eight antibiotics commonly used for the treatment of legionellosis were calculated from the isolates obtained.

Methods: Twelve recreational pools were enrolled between June 2003 and December 2016 and 7221 water samples were taken from three different points of the water network (tank, tap and shower). Legionella culture was performed according to ISO 11731 and 11731-2 standards. MICs of antibiotics were obtained by a gradient test.

Results: 1.44% of the water samples were positive for L. pneumophila. 60 strains (57.69%) were isolated from showers, 26 (25.00%) from tanks and 18 (17.31%) from taps. L. pneumophila counts were <100CFU/L in 75 samples (72.12%), 100-1000CFU/L in 17 (16.35%) and >1000CFU/L in 12 (11.54%). The MIC₉₀ values obtained were for Rifampicin 0.125mg/L; Trimethoprim-Sulfamethoxazole 0.25mg/L; Azithromycin and Levofloxacin 0.5mg/L; Clarithromycin and Ciprofloxacin 1.0mg/L; Doxycycline and Tigecycline 4.0mg/L.

Conclusions: The use of showers in recreational pools can become a potential pathway for exposure to L. pneumophila, even in cold climates. The wild-type MIC distributions presented in this article may be useful for a better detection of antibiotic resistance and can contribute to improvements in the choice of the antibiotic treatment of legionellosis.