Bartonella quintana Endocarditis in Canadian Indigenous Communities Highlights the Need for Outbreak Investigation, Vector Surveillance and Access to Water, Sanitation and Hygiene

To the Editors: We read with great interest Petel et al article on Bartonella quintana endocarditis in a Canadian Indigenous youth, which underscores the endemicity of B. quintana in communities with inadequate access to water, sanitation and hygiene. We commend the authors for shedding light on this issue and wish to provide context regarding B. quintana in Canada, emphasizing the role of sentinel cases in public health interventions. Incorporating vector analysis of body and head lice into outbreak investigations is essential to address this overlooked disease. The incidence of B. quintana in Canada appears to be increasing; 94.1% (32/34) of polymerase chain reaction (PCR)-confirmed cases were reported after 2016 and PCR percent positivity has increased over the last decade.1 While Petel et al. reference a prior case of B. quintana endocarditis in an indigenous child from Manitoba, it is important to note that similar cases have now been documented in 6 indigenous communities spanning thousands of kilometers (Fig. 1).1,4 Since B. quintana has no animal reservoir, each case signals human-to-human transmission within the affected community. Endocarditis is a rare manifestation of B. quintana, likely underreported due to misdiagnosis or the absence of confirmatory PCR testing.1 PCR on blood has an estimated sensitivity of only 30% in B. quintana endocarditis.7 Furthermore, many patients are not deemed to be candidates for valve replacement surgery, precluding the ability to perform PCR on an explanted valve. Thus, the actual disease burden is likely higher than the aforementioned case numbers.7 Seroprevalence studies indicate 15% positivity in communities where cases of endocarditis have been reported.8FIGURE 1.: Published cases of PCR-proven B. quintana infective endocarditis acquired in Canadian indigenous communities. Approximate geographic locations of published cases of PCR-confirmed B. quintana endocarditis in Canadian indigenous communities. Published IE: indicates published case of PCR-proven B. quintana infective endocarditis. Unpublished IE: indicates unpublished cases of B. quintana including those that remained undiagnosed or without PCR-confirmation. Bacteremia/active disease without IE: indicates cases of B. quintana, such as chronic bacteremia and bacilliary angiomatosis, without infective endocarditis. Seropositivity/cleared infection: indicates cases with B. quintana serologic positivity on indirect immunofluorescent antibody testing but without evidence of active disease and thus are not contagious. *Indicates that these disease manifestations are contagious.1–6As everyone with B. quintana endocarditis represents hidden transmission, each identified case should prompt a public health response. Without systematic testing of close contacts, the true disease burden remains unknown. Thankfully, a practical, noninvasive surveillance tool already exists: louse analysis. Our group has piloted the use of body lice to detect B. quintana in Canada.9 While blood PCR often fails to detect infection, lice act as natural incubators, increasing diagnostic sensitivity.1,9 Investigating lice from close contacts of sentinel cases could be an initial step in outbreak investigation, followed by further assessment of households where B. quintana-positive lice are found to identify subclinical endocarditis. Petel et al.’s case also supports the role of head lice in B. quintana transmission. Though controversial, multiple studies in low-resource settings suggest that head lice may serve as vectors. Under conditions of poor sanitation, body lice may migrate and colonize hair and head lice may colonize clothing. Consequently, vector surveillance should include both head and body lice. Insufficient water, sanitation and hygiene access remains a key driver of B. quintana transmission in Indigenous communities, as lice can be effectively controlled through regular laundry, bathing and pediculicide application. Alarmingly, 19% of published B. quintana endocarditis cases in Canada have been fatal.1 Petel et al.’s case highlights that B. quintana may be more widespread than previously recognized. Implementing vector analysis of body and head lice in outbreak investigations is a critical step toward understanding and addressing this neglected disease.

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