Clinical predictors and outcomes for Legionnaire's disease versus bacteremic pneumococcal pneumonia

Legionnaires' disease (LD) is a serious sometimes fatal pneumonia caused by Legionella pneumophila. The clinical manifestations of LD may be similar to those by caused by Streptococcus pneumoniae. As both conditions can be serious illnesses but requiring different antimicrobial therapies, factors that can help differentiate these types of pneumonias can be helpful in the clinical management of hospitalized patients with bacterial pneumonia. This study aimed to compare clinical features and indicators of disease progression in hospitalized patients with community-acquired pneumonia caused by L. pneumophila and bacteremic S. pneumoniae.

We conducted a retrospective case comparison study of adult patients hospitalized with LD or S. pneumoniae. Data collected included demographic, clinical characteristics, and comorbidities, and outcomes. Data were analyzed using SPS vs 24.0. Multivariable analysis was done using logistic regression with a forward stepwise algorithm.

A total of 106 patients met study criteria. The incidence of LD peaked in summer months and S. pneumoniae peaked in the winter quarter. From multivariable analysis predictors of LD were male gender (OR=21.6, p < 0.001), diarrhea (OR=4.5, p = 0.04), body mass index (BMI) (OR=1.13, p = 0.02), hyponatremia (OR=5.6, p = 0.03 and Charlson weighted index of comorbidity (CWIC) score (OR=0.61, p = 0.01). Patients with S. pneumoniae had higher rates of mechanical ventilation, septic shock, and death than those with LD.

Our data suggests that variables that may distinguish LD from S. pneumoniae include male gender, diarrhea, hyponatremia, higher temperature on admission, higher BMI and fewer comorbidities. Bacteremic S. pneumoniae was associated with poorer outcomes than LD including higher rates of septic shock, mechanical ventilation, ICU admission, and death.