Legionellosis was included in 1996 among notifiable diseases at the national level in Spain (Royal Decree 2210/95). In the Community of Valencia, the Basic Surveillance System, including legionellosis as a Notifiable Disease (OED), was developed by the Ordinance of March 4, 1997. Ten years later, in 2017, 236 cases of legionellosis were declared with an incidence rate of 4.7 cases per 100,000 inhabitants (9).
The national regulation currently in force is the Royal Decree 865/2003, which is an old text (28). Currently, this law notes the culture method described in ISO1173:1998 for the Legionella assay in water samples from cooling towers, but not explicitly for other risk installations. However, culture method is a slow method that can lead to a delay in taking timely steps on the facilities to prevent risk situations (23,28,29).
Although recovery and isolation of Legionella colonies by culture is recognized as the gold standard method, well-known limitations of this method could compromise their utility in preventative or rapid control action. Among these drawbacks, we can highlight: (a) long time to confirm results (from 2 to 28 days are required), (b) changes on environmental water samples have been identified during their transport to laboratory, which might take up to 1–2 days, (c) likely presence of viable and infective but no-culturable cells, (d) poor sensitivity, and (e) a rate of inconclusive results up to 20% by interfering microbiota (30,31).
The new standard UNE 100030: 2017 (29) tries to cover the lag of the Royal Decree by incorporating new technical requirements in the prevention and control of Legionella with the main objective of complementing it. One of the main contributions of the new standard is the explicit recognition of alternative not growth-based methods to the culture for the detection of Legionella, if they meet the specified technical requirements on validation and certification.
Nevertheless, although some technical recommendations are established in section 6.15 of this standard, it is not applicable to facilities of sanitary/therapeutic use, so the development of other complementary initiatives can be expected.
Given the importance of fast detecting the presence of Legionella and knowing the factors that determine the quickly facilities colonization by this bacterium, it is necessary to define a new standard of Legionella determination which is not based on culture method, and also to develop new diagnostic methods.
According to the Royal Decree 865/2003, regulation on the prevention and control of legionellosis in Spain, a temperature between 25°C and 50°C is considered a risk factor for the proliferation and colonization of Legionella. In fact, thermal disinfection (hot water overheating) was the first method used to control Legionella in water distribution systems in hospitals (32,33). Water at 70 °C kills Legionella pneumophila in 10 minutes, while at 60 °C it takes 25 minutes (34). The temperature rise above 60 °C for several days ensures the success and absence of legionellosis (35). Its advantage lies in its minimum cost. However, the loss of heat in some points of the hot water distribution network (heater, recirculation, representative points of use) may cause defective return valves in the faucets, providing generalized temperature losses due to the mixing of cold and hot water. Moreover, although thermal disinfection is the most common, economical and effective treatment for the Legionella control, it does not eliminate the bacterial biofilm, which protects Legionella (36).
In our study, the average temperature is higher in the points of frequent use than those of infrequent use. The importance of maintaining temperatures above 50 °C, and even better above 55 °C (26), is well known.
Furthermore, more Legionella positive results were found using the new standard index than using a single technique, whether it is culture or IMS, only for temperatures around 40–50 °C (data not shown). For this reason, it is important to consider not-growth based diagnostic methods, able of measuring Legionella properties other than its growth in an artificial medium on a plate.
The importance of pipe lenght and water stagnation as risk factors for Legionella colonization have also been studied. These studies were conducted in residential facilities (13). The structural complexity of a health facility suggests means that pipe length, floor and pavilion cannot be used as risk factors, while it is important to consider both a correct and frequent use of terminal points (26) to prevent colonization and formation of biofilms.