Antonio Doménech-Sánchez

Swimming and bathing environments play a crucial role in promoting health, well-being, and social inclusion. The recreational use of water bodies for play and leisure activities presents a unique opportunity for interdisciplinary water research, enabling diverse approaches ranging from chemistry and microbiology to environmental science and public health. This consensus document, developed during the XI International Conference on Swimming Pools and Spas (ICSPS, Athens 2025), highlights shared priorities for safeguarding human and environmental health in aquatic settings. Key objectives include preventing drowning, health risks, and injuries through appropriate design, effective operation, and hygienic behavior. Microbiological quality monitoring is a fundamental requirement for maintaining safety standards and must be complemented by rigorous control of chemical parameters to ensure overall integrity. The document emphasizes the need to reduce chemical use, energy consumption, and water waste while ensuring safety and comfort for users and workers. Addressing sustainability while responding to the challenges posed by climate change and technological innovation represents a key target. The XI ICSPS Consensus Document strongly advocates for a European Directive or International Regulation that provides minimum quality requirements to protect all European citizens’ public health and environment, while embracing a broader global perspective of sustainability and equity for access to waters for recreational uses. This focus is particularly relevant in the European context, where most water-related sectors are already regulated for the protection of public health, yet recreational pools and spas—despite their major socio-economic relevance and central role in tourism—remain without a harmonized framework. Addressing this gap is essential to support safe mobility, responsible leisure, and robust public health protection for all citizens. Harmonized requirements, continuous education of professionals, and innovation through digital engineering tools and artificial intelligence are essential to achieve resilient, safe, and eco-sustainable aquatic facilities. Users’ education is also recognized as a key task for pool management and competent authorities, fostering hygienic behavior, accident prevention, and social responsibility. At any age, swimming pools and spas represent an essential tool in health promotion, encompassing social, mental, and physical wellness, and supporting longevity through social inclusion and adapted physical activity. The international scientific community who conduct research on swimming pools and spas is quite specialized and multidisciplinary but rather narrow, numbering roughly 200 research groups worldwide. The ICSPS network supports progress in research and innovation by promoting effective management, safety, and quality, while also fostering a culture of awareness and responsibility. These advancements strongly advocate for the development of harmonized international policies to ensure consistent standards and sustainable protection across recreational waters in Europe and worldwide.

Pseudomonas aeruginosa is a key indicator of hygienic and operational deficiencies in swimming pools, particularly in tourist facilities with high and variable user loads. This study reports the results of a four-year regulatory surveillance program (2016–2019) assessing P. aeruginosa contamination in tourist swimming pools in Andalusia, Spain. The program involved 14 hotels and 58 unique installations. A total of 2053 water samples collected from different installation types (outdoor and indoor pools, whirlpools, and cold-plunge pools) were analyzed using standardized ISO methods within the framework of Spanish legislation, and prevalence comparisons were based on proportion tests. The overall prevalence of P. aeruginosa was 5.1%, with marked differences among installation types, reflecting both variation in contamination rates and unequal sampling intensity. Whirlpools consistently showed the highest contamination rates, whereas indoor pools and cold-plunge pools exhibited lower prevalence. No significant differences were observed between chlorine- and bromine-treated pools, and contaminated samples were detected across the full range of disinfectant concentrations, including values within regulatory limits. Temporal analysis revealed that apparent seasonal peaks were installation-dependent rather than reflecting a uniform seasonal trend. Winter detections were confined to indoor pools and whirlpools, which remain operational year-round, while outdoor pools and cold-plunge pools were underrepresented during the low season due to reduced sampling. A marked increase in prevalence was observed in 2019, driven mainly by summer months and high-risk installations; however, this rise was not directly associated with tourist volume and does not support causal inference. These findings highlight the importance of installation-specific and operational factors in shaping P. aeruginosa contamination patterns. The study underscores the need for targeted surveillance strategies focusing on high-risk installations and for cautious interpretation of seasonal patterns in datasets derived from routine regulatory monitoring.

Tourist swimming pools are complex aquatic systems where operational failures can favour microbial growth and exposure to opportunistic pathogens. We conducted a four‑year surveillance (2016–2019) in hotel pools across Andalusia (Spain), analysing 2,053 water samples under Spanish regulation (Royal Decree 742/2013) with ISO methods (Pseudalert®/ISO 16266‑2 for Pseudomonas aeruginosa and Colilert‑18/ISO 9308‑2 for Escherichia coli). Overall non‑compliance reached 24.8%, and 2.0% of samples triggered immediate pool closure, most frequently due to P. aeruginosa. The bacterium was detected in 5.1% of samples, with heterogeneous distribution among installations: whirlpools (7.9%) > indoor pools (6.4%) > outdoor pools (4.5%) > cold wells (2.9%). No significant association was observed between use by children and P. aeruginosa detection (p > 0.05). Contamination occurred under both chlorine and bromine disinfection, with comparable prevalence (p = 0.18), and overlapping residual distributions indicated that single‑point disinfectant measurements alone did not predict contamination. Seasonality showed a bimodal pattern with winter (January) and summer (August) peaks, and prevalence markedly increased in 2019 compared with prior years. These findings highlight that P. aeruginosa contamination in tourist pools is driven less by momentary disinfectant levels than by structural and operational determinants (e.g., biofilm‑prone niches and hydraulic performance), underscoring the need for continuous surveillance, hydraulic optimization, routine mechanical cleaning, and robust monitoring across all seasons.

Indoors, the infection risk of diseases transmitted through the airborne route is estimated from indoor carbon dioxide (CO₂) levels. However, the approaches to assess this risk do not account for the airborne concentration of pathogens, among other limitations. In this study, we analyzed the relationship between airborne SARS-CoV-2 levels and environmental parameters. Bioaerosols were sampled (n = 40) in hospital corridors of two wards differing in the COVID-19 severity of the admitted patients. SARS-CoV-2 levels were quantified using droplet digital PCR. SARS-CoV-2 was detected in 60% of the total air samples. The ward where the mildly ill patients were admitted had a higher occupancy, transit of people in the corridor, and CO₂ levels, but there were no significant differences in SARS-CoV-2 detection between wards. The mean CO₂ concentration in the positive samples was 569 ± 35.6 ppm. Considering all samples, the CO₂ levels in the corridor were positively correlated with patient door openings but inversely correlated with SARS-CoV-2 levels. In conclusion, airborne SARS-CoV-2 can be detected indoors with optimal ventilation, and its levels do not scale with CO₂ concentration in hospital corridors. Therefore, CO₂ assessment should not be interpreted as a surrogate of airborne viral presence in all indoor spaces.

The COVID-19 pandemic prompted widespread adoption of intensified hand hygiene practices, raising concerns about their medium-term impact on the skin microbiome. This study investigates alterations in the hand microbiome of healthy adults during the pandemic compared to pre-pandemic periods in Majorca, Spain. A total of 30 volunteers (16 women, 14 men; mean age 44.1 ± 8.8 years) were sampled between 2014 and 2021. Palm swabs were collected following WHO guidelines, alongside measurements of skin pH, temperature, and handwashing frequency. Bacterial DNA was extracted and analyzed via 16S rRNA (V3-V4) metagenomic sequencing to assess microbial diversity and composition. Results revealed a significant decline in microbial diversity during the COVID-19 period, accompanied by a marked shift in the community structure. The Firmicutes phylum dominated, with Bacillales increasing from 30.7% to 84.1%, primarily driven by a surge in Staphylococcus species (e.g., S. pasteuri). Conversely, S. hominis and Actinomycetales nearly disappeared. No significant associations were observed with gender or handwashing frequency. The skin temperature increased during the pandemic, while the pH remained stable. The Staphylococcus/Bacillus ratio shifted significantly, favoring Staphylococcus dominance. These findings, derived from a geographically limited population in Majorca, Spain, demonstrate that stringent hygiene measures during COVID-19 reduced microbial diversity and restructured hand microbiome composition. The study underscores the necessity for balanced hygiene strategies that mitigate pathogen transmission while preserving beneficial microbial communities critical to skin health.

Pseudomonas aeruginosa is a common pathogen associated with recreational water facilities and poses risks to public health. However, data on the prevalence of P. aeruginosa in tourist destinations like the Canary Islands, Spain, remain limited. We assessed P. aeruginosa prevalence in 23 tourist facilities from 2016 to 2019. Compliance with water quality standards was evaluated, and 3962 samples were collected and analyzed. We examined different types of recreational water installations, including outer swimming pools, whirlpools, and cold wells. Of the sampled facilities, 31.2% did not comply with the current legislation’s parametric values, mainly due to inadequate disinfectant levels, water temperature, and P. aeruginosa presence. The prevalence of P. aeruginosa was 4.8%, comparable to some European countries but lower than others. Cold wells displayed the highest non-compliance rate (89.2%) and yet exhibited a lower P. aeruginosa prevalence (1.9%) than outer swimming pools and whirlpools. Children’s presence did not significantly impact P. aeruginosa contamination. Chlorine-based disinfectants are more effective than bromine-based ones in controlling P. aeruginosa. Regional variability in contamination was observed, with Fuerteventura showing lower colonization rates. Disinfectant levels play a critical role in P. aeruginosa control, and maintaining adequate levels is essential, particularly in bromine-treated installations. Our findings provide valuable insights into the prevalence and distribution of P. aeruginosa in recreational waters within tourist facilities. Tailored strategies are needed to ensure water safety in different Spanish regions. Continued monitoring and assessment, combined with artificial intelligence and machine learning, will enable the implementation of targeted interventions to protect the health of recreational water users.

The increasing emergence of multidrug resistant isolates of P. aeruginosa causes major problems in hospitals worldwide. This concern is particularly significant in bloodstream infections that progress rapidly, with a high number of deaths within the first hours and without time to select the most appropriate treatment. In fact, despite improvements in antimicrobial therapy and hospital care, P. aeruginosa bacteremia remains fatal in about 30% of cases. The complement system is a main defensive mechanism in blood against this pathogen. This system can mark bacteria for phagocytosis or directly lyse it via the insertion of a membrane attack complex in the bacterial membrane. P. aeruginosa exploits different strategies to resist complement attack. In this review for the special issue on “bacterial pathogens associated with bacteriemia”, we present an overview of the interactions between P. aeruginosa and the complement components and strategies used by this pathogen to prevent recognition and killing by the complement system. A thorough understanding of these interactions will be critical in order to develop drugs to counteract bacterial evasion mechanisms.

Phage lysins are a promising alternative to common antibiotic chemotherapy. However, they have been regarded as less effective against Gram-negative pathogens unless engineered, e.g., by fusing them to antimicrobial peptides (AMPs). AMPs themselves pose an alternative to antibiotics. In this work, AMP P87, previously derived from a phage lysin (Pae87) with a presumed nonenzymatic mode-of-action, was investigated to improve its antibacterial activity. Five modifications were designed to maximize the hydrophobic moment and net charge, producing the modified peptide P88, which was evaluated in terms of bactericidal activity, cytotoxicity, MICs or synergy with antibiotics. P88 had a better bactericidal performance than P87 (an average of 6.0 vs. 1.5 log-killing activity on Pseudomonas aeruginosa strains treated with 10 µM). This did not correlate with a dramatic increase in cytotoxicity as assayed on A549 cell cultures. P88 was active against a range of P. aeruginosa isolates, with no intrinsic resistance factors identified. Synergy with some antibiotics was observed in vitro, in complex media, and in a respiratory infection mouse model. Therefore, P88 can be a new addition to the therapeutic toolbox of alternative antimicrobials against Gram-negative pathogens as a sole therapeutic, a complement to antibiotics, or a part to engineer proteinaceous antimicrobials.