Outbreak of Travel-Related Pontiac Fever Among Hotel Guests Illustrating the Need for Better Diagnostic Tests

Gregory D. Huhn; Barb Adam; Roger Ruden; Lisa Hilliard; Pam Kirkpatrick; Jeffrey Todd; William Crafts; Douglas Passaro; Mark S. Dworkin


J Travel Med. 2005;12(4):173-179. 

In This Article

Abstract and Introduction

Background: Pontiac fever (PF), a legionellosis with influenza-like symptoms and high attack rates, is rarely reported. Travel-related outbreaks can elude detection because infected persons are often widely removed geographically from the transmission source before illness onset. Thirty-one persons staying at an Illinois hotel during August 9 to 11, 2002, reported influenza-like symptoms to local health departments within 24 to 48 hours of checkout. We investigated to identify the cause and source of illness to guide control measures.
Methods: Hotel water samples were collected for culture. A telephone questionnaire detailing illness symptoms and exposures was administered to all who were guests at the hotel from August 9 to 15 (n = 380). A case was defined as onset of fever, headache, and myalgia in a guest in the 14 days following the hotel stay. Patient sera were tested by hemagglutination assay for antibodies to Legionella species.
Results: Among 204 questionnaire respondents from 15 states and Canada, 50 met the case definition. Among persons exposed to the swimming pool/whirlpool spa area, 63% (47 of 75) became ill versus 3% (3 of 110) of unexposed persons (relative risk 23.0, 95% CI 7.4-71.1). Illness risk increased with increasing time exposed to the pool/spa. Approximately 95 to 115 bathers per day, two to three times above the usual number, used the spa during August 9 to 11. Three Legionella species, L. dumoffii, L. maceachernii, and L. micdadei, were isolated from spa filter backwash cultures. Two of 15 ill persons with acute- and convalescent-phase sera had a greater than fourfold rise in antibody titer to L. micdadei.
Conclusions: PF was associated with exposure to a hotel pool/spa area. Heavy bather usage likely contributed to a decreased effectiveness of the disinfectant in the whirlpool spa, possibly promoting bacterial aerosolization. Linking case information from many states is essential in identifying and eliminating the source of disease transmission in travel-related outbreaks of PF. Clinicians should be aware of PF in the differential diagnosis of patients with influenza-like symptoms following recent travel, particularly with exposure to a communal-use whirlpool spa.

Infection with Legionella species can manifest in two distinct forms, the pneumonic form, legionnaires' disease (LD), and the nonpneumonic form, primarily Pontiac fever (PF).[1,2,3,4,5] In the United States, an estimated 8,000 to 18,000 cases of community-acquired legionellosis occur annually; however, the Centers for Disease Control and Prevention (CDC) estimates that < 10% of total cases, predominantly LD, are reported to public health officials.[6] In contrast to the more severe LD, PF is a self-limited illness with higher attack rates in outbreak settings. Travel-related outbreaks of legionellosis are rarely reported and frequently elude detection. Infected persons are often widely removed geographically from the transmission source before onset of illness, which may be up to 3 days for PF and 14 days for LD.[7,8]

Approximately 50% of the 48 species of Legionella and 70 distinct serogroups identified have been associated with human disease.[9] Serologic and urinary antigen tests are the primary tools in the laboratory diagnosis of PF. Validated serologic testing for the majority of the 70 serogroups have not been fully developed, and only Legionella pneumophila serogroup 1 (LP1) can be reliably assayed by urinary antigen tests.[10,11,12] In the past 20 years, the reliance on rapid urine antigen tests in the diagnosis of legionellosis has hindered investigations of non-LP1 legionellosis outbreaks.[13]

We summarize an investigation of a travel-related outbreak of PF associated with a nonpneumophila species of Legionella. The investigation underscores the challenges in the diagnosis of PF and highlights the factors involved in linking case information from many states, which is critical in identifying and eliminating sources of disease transmission in a travel-associated outbreak.


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