Between 80 to 90 percent of reported cases of Legionnaires' disease are caused by L. pneumophila sg1. L. pneumophila sg 2-14, on the other hand, accounts for somewhere between 15 to 20 percent of Legionnaires’ disease cases. However, this strain is more commonly found in the environment. What, then, accounts for the discrepancy between the number of cases caused by each strain? 

In order to better understand this discrepancy, Italian researchers investigated the virulence of Legionella pneumophila strains in the water found in hospitals located in Northern Italy, the results of which can be found in the study entitled “Virulence of Legionella pneumophila strains isolated from hospital water system and healthcare-associated Legionnaires’ disease in Northern Italy between 2004 and 2009.”

A substantial number of Legionnaires' disease cases can be traced back to exposure to contaminated water found in hospital water systems. Majority of these cases are caused by the L. pneumophila sg1 strain.

To date, experts and authorities have to settle on a specific set of guidelines pertaining to Legionella testing in the hospital environment.

There are some experts who advocate diagnostic testing and pneumonia surveillance in assessing the quality of hospital water systems. The American Centers for Disease Control and Prevention, on the other hand, recommends clinical surveillance over environmental surveillance, save for transplant units. On their end, French authorities employ strategies based on assessing the number of microorganisms, including Legionella bacteria, found in hospital water systems.

Italian health authorities subject Legionnaires' disease to special surveillance procedures wherein practitioners must report new cases, whether the disease is contracted from a hospital or from a community. Once local authorities have been alerted, the information is then passed on to regional authorities, which in turn pass the report to the appropriate agencies in the national level. In the last decade, a total number of 164 cases of Legionnaires' disease contracted from a hospital setting have been reported from Piemonte. Of this number, 112 cases were traced backed to two major hospitals in the area.

Italian researchers hypothesised that this discrepancy may have been caused by the fact that the bacterial strain found in these hospitals were more pathogenic as compared to those found in other hospitals. Furthermore, the higher virulence potential of this particular strain may be attributed to the fact that the bacteria are more likely to survive in water that is in the form of aerosols. 

The researchers suggest that hospitals with more virulent strains of the bacteria should intensify monitoring and implement strategies designed to control contamination. Finally, the researchers recommend that hospital authorities should also pay attention to the specific bacteria strain found, as each strain has a different capacity in causing Legionnaires' disease. By focusing on this last key area, authorities can better respond and implement effective intervention.

+Duncan Hollis