A question we are asked all the time is, “How likely is it that my symptoms are caused by Bartonella species?”

This is a very difficult question to answer. The number of people who have been infected by Bartonella species in the general population is different than the number of people affected by particular symptoms. The number may also be different based on where people live or travel, or if they have a high-risk job that involves working outdoors or in a veterinary clinic.

When studies of Bartonella species infection are made, they usually look at “prevalence.” Prevalence is the number of cases that are present in a population at any given time. Another kind of study is “incidence,” which looks at the likelihood of becoming infected during a given time period. For example, comparing the percentage of people who get the flu each month is a study of “incidence.”

Researchers have different methods available to measure how many people have been infected with Bartonella species. Methods may use blood tests like antibodies (serology) or DNA testing (PCR). They may also use medical record reviews or insurance claim information.

So what information is available regarding the prevalence and incidence of Bartonella species infections in various groups of people? A few key studies that you should know about include:

Key Patient Population
Research Study
Healthy Individuals
Bartonella spp bacteremia in blood donors
This study of 500 blood donors in Brazil provides a population baseline figure regarding both active infection (bacteremia) and exposure to past infection. Using Bartonella ePCR and Bartonella IFA test methods, the researchers found DNA in 3.2% and antibodies to B. henselae and B. quintana in 16% and 32% of healthy blood donors. This research helps show that healthy individuals can be actively infected with Bartonella species, but show no symptoms. Importantly, this study showed little overlap between positive DNA results and positive antibody results. This is one study that we would like to replicate in the United States.
High Risk Individuals
Detection of Bartonella species in the blood of veterinarians and veterinary technicians: a newly recognized occupational hazard?
This study used Bartonella ePCR and sequencing to determine the presence of Bartonella DNA in the blood of 114 veterinary personnel compared to 32 non-veterinary controls in the United States. The Duke and NCSU researchers found that 28% of veterinary participants were infected with at least one Bartonella species. None of the healthy controls tested positive. Infected veterinary workers were also almost twice as likely to report headaches and irritability as uninfected individuals. The results of this study suggest that Bartonella species infection is an occupational safety concern for veterinary workers in the United States. This study design was applied to Spanish veterinary workers as well, but yielded very different results, suggesting that geography is important for prevalence.
Cat Scratch Disease (CSD)
Cat-Scratch Disease in the United States, 2005-2013
This study by researchers at the Center for Disease Control (CDC) used insurance claims data to investigate the incidence of cat scratch disease (CSD) in the United States, using a single clinical diagnostic code (ICD code). They found that incidence of CSD (B. henselae infection) is highest in the Southern states followed by the East North Central states, and the far Western states. They also found peak seasonal diagnoses occurred in January and in early fall and there was higher than expected prevalence among adults compared to children and older people. The data for this study were rather limited, so caution should be taken in generalizing results to the broader US population. However, the results clearly point to important geographic and seasonal patterns in clinical diagnosis of CSD.
Rheumatic Patients
Bartonella spp. bacteremia and rheumatic symptoms in patients from Lyme disease-endemic region
This retrospective study from 2011 documented high active infection and seroprevalence in a sample of 296 patients with a variety of prior diagnoses and rheumatic symptoms. Study participants were tested for both DNA and antibodies to Bartonella species using Bartonella ePCR and IFA test methods. Results showed that 41.1% were actively infected and 62% showed seroprevalence of multiple Bartonella species, with very little overlap between groups. The results of this study are compelling, suggesting an important role for Bartonella species in rheumatic diseases, such as Rheumatoid Arthritis (RA). Furthermore, Bartonella could be involved in cases of persistent Lyme Disease or potential misdiagnosis.
Culture-Negative Endocarditis Patients
Bartonella, a common cause of endocarditis: a report on 106 cases and review
This study of 106 cases in France aimed to identify specific diagnostic criteria that should be used when diagnosing Bartonella endocarditis. Bartonella species were discovered as a major cause of blood culture-negative endocarditis in HIV patients less than 30 years ago. Blood culture-negative cases represent up to 31% of all endocarditis cases and carry a high mortality rate of over 20%. All too often, diagnosis is confirmed only after the surgical removal of a heart valve. The authors concluded that increasing reports of Bartonella endocarditis are likely due to the advancement of diagnostics, interest, and understanding of bartonellosis rather than a true increase in incidence.
Immunocompromised Transplant Patients
Seroprevalence of Bartonella henselae in patients awaiting heart transplant in Southern Italy
Immunocompromised people who undergo organ transplant are at risk for life-threatening bacterial infections. For example, B. henselae can cause severe disseminated disease in solid organ transplant patients. This retrospective study found that 21% of patients awaiting a heart transplant in Italy were seropositive for B. henselae. Specifically, 8% were positive for IgM antibodies, and13% were positive for IgG antibodies. None of the healthy controls tested positive. Despite the small number of participants, the researchers suggested that Bartonella should be included in routine screening analyses of opportunistic infections for pre-transplant patients.
Neuro-Psychological Patients
Infections and Childhood Psychiatric Disorders: Tick-Borne Illness and Bipolar Disorder in Youth
Inflammation is suspected to play a role in psychiatric illness, but research on initiating pathogens is limited. This study aimed to elucidate the role of tick-borne illnesses (TBI) in pediatric bipolar disorder (PBD). Children between the ages 4 and 12 who were previously diagnosed with variable levels of bipolar disorder were tested for TBI. Results showed that 74% of patients diagnosed with PBD were also seropositive for TBI such as Babesia, Borrelia, and Bartonella. Interestingly, the majority of the patients that tested positive for TBIs did not recall a tick bite in the past. The authors suggested that TBI should considered when treating psychiatric disorders, especially for unresponsive or partially responsive cases.

This research is considered to be in its very early stage from an expert, scientific perspective. Despite significant gaps in the literature, these studies are compelling and suggest that bartonellosis (symptomatic infection by Bartonella species) plays a much bigger role in chronic diseases than currently appreciated. This includes diseases in people considered “immunocompetent,” that is, people who do not have conditions that impair their immune system, such as HIV infection or many cancer treatments. Bartonella species are increasingly implicated in a wide spectrum of diseases including neurovascular, cardiovascular, rheumatic and hematological disorders.

Our mission is to work with our research partners to better clarify the clinical importance of bartonellosis in key patient populations. Of particular importance are studies that answer practical clinical questions to better guide physicians in the diagnosis and treatment of this very important emerging infectious disease.

To learn more about Bartonella, see our free medical webinar Understanding Bartonella, available on our YouTube channel or through CDC TRAIN.