Data from the first 3 years of the Center for Disease Control and Prevention’s Active Bacterial Core surveillance (ABCs) program on legionellosis confirm that incidences of disease caused by the bacteria are increasing across the United States, according to the latest Morbidity and Mortality Weekly Report (MMWR. 2015 Oct 30;64:1190-1193).
The ABCs program, which launched in 2011, identified 1,426 cases of legionellosis over the 3-year time span, and incidence rates of 1.3 (2011), 1.1 (2012), and 1.4 (2013) cases per 100,000 individuals in the general population. This corroborates similar findings made by the National Notifiable Diseases Surveillance System (NNDSS) between 2000 and 2011, which reported an increase in the crude incidence rate of legionellosis nationwide from 0.39 to 1.36 cases per 100,000 individuals.
The two main clinical syndromes associated with legionellosis are Legionnaires’ disease, which is a severe form of pneumonia; and Pontiac fever, a milder illness without pneumonia.
“During 2000-2011, passive surveillance for legionellosis in the United States demonstrated a 249% increase in crude incidence, although little was known about the clinical course and method of diagnosis,” says the report, led by Dr. Kathleen I. Dooling of the CDC’s National Center for Immunization and Respiratory Diseases.
The report also states that “ABCs data during 2011-2013 showed that approximately 44% of patients with legionellosis required intensive care, and 9% died.” Furthermore, incidence increased with age among the ABCs program cohort. Those younger than 50 years of age had a 0.4 incidence rate per 100,000 individuals; patients between 50 and 64 years old had a 2.5 per 100,000 incidence rate; those who were 65-79 years old had a 3.6 per 100,000 incidence rate; and individuals 80 years and older had an incidence rate of 4.7 per 100,000 individuals.
“Among cases identified during 2011-2013, 79% occurred in persons aged >50 years, 65% were in males, and 72% of patients were white,” says the report, adding that “1,300 (91%) received a diagnosis of legionellosis on the basis of urine antigen testing, which only detects Lp1 species.”
The ABCs program defined a confirmed case of legionellosis as “the isolation of Legionella from respiratory culture, detection of Legionella antigen in urine, or seroconversion (a more than fourfold rise in antibody titer between acute and convalescent sera) to Lp1.” Unlike NNDSS, ABCs recorded clinical and race data for each patient found to have legionellosis, finding that incidence rates among blacks were higher than among whites per 100,000 individuals: 1.0 vs. 1.5, respectively.
The report concludes by calling for further research into the disparities in legionellosis cases based on race, age, and geography, as well as the need for “more sensitive laboratory tests for legionellosis because proper diagnosis is needed for treatment and public health action.”
This study was supported by the CDC.