Bartonella quintana is a pathogenic bacterium carried and transmitted to humans by the body louse, Pediculus humanus humanus. Clinical manifestations of disease are relapsing fever, bacillary angiomatosis, chronic bacteremia, and endocarditis (1). B. quintana infections are not nationally notifiable and little is known regarding their incidence and geographic distribution. Barriers to healthcare access in affected human populations and inherent diagnostic challenges might both contribute to underdiagnosis of cases (2). However, recent cases have been reported among persons experiencing homelessness (PEH) in New York, New York, and Denver, Colorado, USA (1,3).

The Infectious Diseases Society of America’s Emerging Infections Network (EIN) is a healthcare provider–based sentinel network that has >2,800 infectious disease specialists throughout North America (4). We evaluated provider-diagnosed B. quintana infections reported by EIN members to identify opportunities for improving disease awareness and patient diagnosis.

We sent a 6-question survey to EIN members to collect data regarding B. quintana cases, affected populations, and diagnostic challenges (Appendix). We distributed the questionnaire through an electronic mailing list on January 18, 2024, and sent reminder emails on January 25 and February 7. A total of 240 members from 41 US states and the District of Columbia responded; 61 (25%) respondents from 24 states and the District of Columbia stated that they had seen >1 case of B. quintana infection within the previous 10 years (Table), and 47 (20%) noted that cases occurred primarily in PEH communities. Other, nonmutually exclusive affected populations included persons with substance use disorders, mental health disorders, HIV infection, and refugee or rural indigenous populations. The most frequently reported obstacles to earlier diagnosis of B. quintana infection were the lack of clinical suspicion (88%), knowledge about diagnostic tests (73%), and access to B. quintana-specific diagnostic tests (51%). Other challenges included long laboratory turnaround times and inconsistent access to healthcare among affected populations. Free-text responses indicated the value of general clinical knowledge about B. quintana infection. For example, one respondent commented, “I have a strong clinical suspicion that there is an association with other endovascular infections that we sometimes miss clinically. For example, a hemorrhagic stroke in someone with a history of homelessness should raise suspicion of this infection. Additionally, any mycotic aneurysm, particularly of the thoracic or abdominal aorta, should raise suspicion for B. quintana infection.”

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Figure. Map indicating numbers and locations of infectious disease physicians responding to survey regarding Bartonella quintanainfection cases, United States, 2014–2024. US states and territories are indicated. The...

We believe that EIN members are seeing B. quintana cases in diverse geographic locations across the United States, including in the Southeast (Figure), where B. quintana has not been described in the literature (2,5). We also believe that those findings highlight the importance of increasing clinician awareness of possible B. quintana infections among patients at risk for body louse infestation across the United States.

Diagnosis of a B. quintana infection is challenging because of serologic cross-reactivity with other Bartonella spp. and the specific conditions required for a bacterial culture. Several studies suggest that laboratory confirmation could be improved by using molecular testing for detection instead of serologic and culture methods (6,7). Intentional collaboration between healthcare providers and clinical microbiology laboratories could result in earlier diagnosis and improved treatment outcomes, especially the use of reflexive B. quintana molecular diagnostic assays for PEH seeking care for fever of unknown etiology in emergency departments (2).

PEH are disproportionately affected by B. quintana infections, although several other communities are impacted in the United States (1–3). Co-existing medical conditions (e.g., behavioral health conditions) and socioeconomic barriers beyond housing instability, such as lack of medical insurance, can further complicate clinical management (1). Inconsistent access to running water, showers, and laundry facilities with hot water increases the risk for body lice infestation. Limited access to healthcare increases the risk for undiagnosed and untreated B. quintana infections that can lead to severe disease. Recognizing complex social determinants of health provides an opportunity to improve prevention, detection, and treatment of B. quintana infections.

The first limitation of our study is that, although querying EIN members is an efficient and convenient method to hear from infectious disease specialists, those members are not representative of all healthcare providers in the United States. Second, the EIN members who did respond might not have recalled all of their B. quintana cases. Also, reported case locations might have differed from the providers' current practice location.

In conclusion, we consider it critical to increase awareness of B. quintana infection risk among certain patient populations, such as PEH, across the United States and increase awareness of diagnostic testing that would most effectively detect active B. quintana infections. Promoting early recognition and diagnosis of B. quintana infections could result in earlier treatment and improve health outcomes among affected populations.

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Suggested citation for this article: Louis S, Marx G, Hinckley AF, Rich SN, Beekmann SE, Polgreen PM, et al. Perspectives of infectious disease physicians on Bartonella quintana cases, United States, 2014–2024. Emerg Infect Dis. 2024 Dec [date cited]. https://doi.org/10.3201/eid3012.240655