Legionnaires’ disease
Since 2008, the EU case definition focuses solely on Legionnaires’ disease, dismissing Pontiac fever cases. Therefore, the present disease outcome tree focuses only on Legionnaires’ disease and its sequelae.
Legionnaires’ disease is mostly observed in the elderly and conditions associated with immunodeficiency constitute a risk for Legionnaires’.
In rare cases, Legionnaires’ disease may also cause extra-pulmonary symptoms, mainly developing cardiac complications (WHO, 2007). Myocarditis, pericarditis, post-cardiomyotomy syndrome or endocarditis are examples of such manifestations although, according to other studies, most of these complication are related to nosocomial infections (Stout, 1997). Extra-pulmonary manifestations are also often observed in immunocompromised patients. For the purpose of this disease model, we focus on community-acquired Legionnaires’ cases and extra-pulmonary manifestations are excluded.
Legionnaires’ disease causes acute consolidating pneumonia. In most cases, and without testing for the causative agent, pneumonia arising from infection with Legionella pneumophila cannot be distinguished from other types of pneumonia. Symptoms of Legionnaires’ disease are an unproductive cough, chest pain, shortness of breath, myalgia and digestive symptoms such as diarrhoea, vomiting and nausea. Patients may also present neurological symptoms such as confusion or deliria (WHO, 2007).
In many cases, the acute phase requires admission to hospital. Studies have shown that in-patient stays in the hospital vary between eight and 13 days (Lettinga, 2002a; von Baum, 2008). However, it may take more than 90 days to recover to the premorbid health state (Lettinga, 2002a) and roentgenographic clearance can take 2–4 months (Edelstein, 2008). For the model the duration of acute Legionnaires’ disease is set at 8–13 days, as stated in one European study (Lettinga, 2002a).
We consider three different health states occurring during the acute phase of the disease, mild (outpatient, uncomplicated cases), moderate (hospitalised, complicated cases not admitted to an intensive-care unit) and severe (complicated cases admitted to an intensive care unit). Studies have shown that hospitalisation is required in 69–74% of Legionnaires’ cases (von Baum, 2008; Garcia-Fulgueiras, 2003). We therefore assume that 26–31% of cases will be mild. Moreover, it is shown that 30% of hospitalised cases require a stay in an intensive-care unit (ICU) (Lettinga, 2002b), thus the proportion of complicated cases (not requiring ICU) is set to 46.7–53.2% and those requiring ICU is set to 20.7–22.2% of all symptomatic infections.
The case-fatality proportion (CFP) differs widely and is associated with the severity level. The CFP for severe cases was found to be higher, ranging from 10 to 30% (Lettinga, 2002b; Benin, 2002; Falco, 1991). In a review conducted by WHO, case-fatality proportions of community-acquired infections ranged from 5 to 10% (WHO, 2007; Benin, 2002; Howden, 2003). The European working group on Legionella infections (EWGLI) suggested a 12% case-fatality in Europe (von Baum, 2008). In our model, CFP for uncomplicated and complicated cases not requiring a stay in an ICU is set at 5–12% and 10–30% for severe cases requiring an ICU.
Risk of complications
Legionnaires’ disease is associated with pulmonary (e.g. severe respiratory failure, pulmonary abscess and pleural empyema), cardiac (e.g. acute pericarditis, myocarditis), neuromuscular (e.g. headache, confusion, fatigue) and renal (e.g. acute renal failure, interstitial nephritis) complications. Multi-organ involvement or septic shock are also possible. In the outcome-tree these complications are not treated separately as they are part of the acute phase of Legionnaires’ disease.
Studies on the long-term sequelae of Legionnaires’ are scarce, however some reported consequences up to two years after the initial infection (Lattimer, 1979). Two studies reported fatigue in 58–81% of cases, concentration problems and memory loss in 6–81%, muscle/joint pain or muscle weakness in 25–79% and post-traumatic stress disorder in 15% (Lattimer, 1979; Lettinga, 2002a). Given the lack of evidence on the causality of Legionnaires’ and the long-term consequences, these were not considered.
Model input summary
Table 1. Transition probabilities and distributions used in the outcome tree
Health outcome |
Distribution of health states in health outcome |
Transition probability |
Source/assumption |
Symptomatic infection (Uncomplicated) (Complicated) (Complicated ICU) |
46.7–53.2% 20.7–22.2% |
|
von Baum, 2008; Garcia-Fulgueiras, 2003; Lettinga, 2002b |
Fatal cases (Uncomplicated) (Complicated) (Complicated ICU) |
|
5–12% 5–12% 10–30% |
Lettinga, 2002b; Benin, 2002; Falco, 1991; WHO, 2007; Benin, 2002; Howden, 2003; von Baum, 2008 |
Table 2. Disability weights and duration
Health
outcome |
Disability Weight (DW) (Haagsma, 2015) |
Duration |
||
DW |
Label |
In years |
Source |
|
Symptomatic infection (Uncomplicated) (Complicated) (Complicated ICU) |
0.051 (0.039–0.06) 0.125 (0.104–0.152) 0.655 (0.579–0.727) |
Infectious
disease, acute episode, moderate |
0.022–0.036 |
Lettinga, 2002a; von Baum, 2008 |
|
References
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