Healthy Indoors Magazine
Issue link: https://hi.iaq.net/i/289980
Healthy Indoors 33 ublic health agencies focus only on outbreaks of Legionnaires' disease (LD); single sporadic community acquired cases are recorded and examined to see if other cases ap- pear to be associated. Tying together cases of LD where exposure may have occurred over the course of many months with varying incuba- tion times can be very difficult, especially if the source exposes a large number of people. If this first hurdle of associating individual cases of disease to put together evidence of an out- break is not cleared, then no further action is typically taken by public health agencies. So, unless the local emergency room is inundated with unusually high numbers of pneumonias and the clinicians test specifically for Legion- naires disease, there is a good chance that an outbreak will not be detected. Within healthcare settings there are supposed to be in-house specialists to investigate all infections acquired during a patient's stay. Infection Preventionists (IPs) use the term "high index of suspicion," which is supposed to prompt physicians to order tests specifically needed to determine if a patient's pneumonia is caused by Legionella pneumophila. Setting aside the perceived disincentive to diagnose LD in healthcare facilities, the diagnostic tests they must rely upon each have their own signifi- cant limitations. The gold standard of sputum culture and isolation of Legionella bacteria from a patient's sputum or lung biopsies can take from 7 to 10 days for analysis. The rapid urine antigen assay (UAA), which can deliver results in hours, is only capable of detecting Legionella pneumophila serogroup 1 (LP1);if the patient has contracted a different strain of Legionella then the test will be negative. Based on cur- rent information, researchers believe that most (>95%) cases of LD are caused by LP1, but we need to understand that a negative UAA test is expected to miss at least those 5% of cases caused by a different strain. For these and other reasons it is widely ac- P