Bartonella is not contagious through casual person-to-person contact. You cannot catch it from someone who is infected through coughing, sneezing, sharing food, or being in the same room. The bacteria spread to humans almost exclusively through insect vectors (fleas, body lice, sand flies) or through direct contact with infected animals, particularly cats. There is, however, one important indirect route that involves human-to-human spread, and a few rare scenarios worth understanding.
How Bartonella Actually Spreads
There are several Bartonella species that infect humans, and each has its own primary transmission route. The most common species in the United States, Bartonella henselae, spreads through the scratch or bite of domestic or feral cats, especially kittens. Cats carry fleas infected with the bacteria, and when a cat scratches you, flea feces contaminated with Bartonella can enter the wound. An infected cat that licks an open wound can also transmit it.
Bartonella quintana, the species that causes trench fever, spreads through human body lice. This is the one scenario where transmission moves between people, though not directly. Body lice pass from person to person through close physical contact or shared clothing and bedding. The lice carry the bacteria and transmit them when they bite or when their feces are scratched into the skin. So while the bacteria technically move through a human population, they still require the louse as an intermediary. You won’t catch B. quintana from an infected person’s breath, saliva, or touch.
A third species, Bartonella bacilliformis, is transmitted by sand fly bites and is found primarily in the Andes region of South America. The CDC states there is no evidence that ticks transmit any Bartonella species to people.
The Body Lice Exception
B. quintana outbreaks tend to occur in settings with high population density and poor sanitation, where body lice infestations can spread easily. Homeless populations, refugee camps, and historically, soldiers in trenches during World War I have been affected. In these environments, lice move between people through prolonged close contact or shared fabric, creating chains of transmission that look person-to-person but are always mediated by the louse itself.
Preventing this type of spread comes down to controlling lice. Regular access to clean clothing and bedding, the ability to bathe, and avoiding sharing garments with someone who has a lice infestation are the key protective measures.
Blood Transfusion and Transplant Risks
One genuinely concerning route involves blood products. Research from a Brazilian team found Bartonella henselae in 1.2% of 500 blood donors tested, and detected bacterial DNA in 3.2% of those samples. In laboratory studies, B. henselae survived in stored red blood cell units for 35 days at standard refrigeration temperatures. When mice received transfusions from Bartonella-infected donor mice, half of the recipients tested positive for the bacteria afterward, even when the donor animals had no detectable infection in their blood at the time of the transfusion.
Human transmission of B. bacilliformis through blood has been documented, and solid organ transplant recipients have developed Bartonella infections with sometimes fatal outcomes. These findings have led researchers to flag Bartonella as a pathogen that warrants screening consideration in blood donation, though routine screening is not yet standard practice in most countries.
Vertical Transmission During Pregnancy
A small number of case reports suggest Bartonella can pass from a pregnant woman to her fetus. In one case, B. henselae DNA was detected in the blood and tissue of a mother, her husband, and their twin sons conceived through in vitro fertilization. One of the newborns died nine days after birth from a congenital heart defect. The mother had experienced difficulty conceiving, raising questions about whether the infection played a role in her reproductive difficulties.
In another case, a newborn presented with anemia, jaundice, and an enlarged liver and spleen from birth. Genetic testing confirmed B. henselae in both the child’s blood and liver tissue, as well as in the mother’s blood, with identical bacterial sequences pointing to vertical transmission. Vertical transmission of B. bacilliformis has also been reported in a newborn whose mother had active skin lesions from chronic Bartonella infection.
These cases are rare. A 19-year surveillance study in Israel tracked eight pregnant women diagnosed with cat scratch disease. One had a miscarriage with no proven link to the infection, and the remaining seven delivered without complications or signs of infection in their newborns. Still, the evidence is enough that some researchers have called for evaluating Bartonella’s role in women who experience recurrent pregnancy loss.
Why Diagnosis Takes So Long
One reason Bartonella infections cause confusion is that the bacteria are extremely slow-growing and difficult to detect. If a blood culture is ordered, it needs to be held for at least 21 days before it can be considered negative. Blood-based molecular tests (which look for bacterial DNA) have limited sensitivity, meaning a negative result does not rule out infection. Serology, which tests for antibodies, can help but may give misleading results because different Bartonella species cross-react with each other.
The most reliable diagnostic window comes from testing lymph node tissue directly, though this is typically reserved for cases where the diagnosis is unclear or the patient needs the fluid drained to relieve pain and swelling. In cases of heart valve infection, excised valve tissue can be tested to confirm the diagnosis.
Practical Takeaways for Household Contacts
If someone in your household has a Bartonella infection, you do not need to isolate from them or take special precautions around their dishes, laundry, or personal items (with the exception of body lice scenarios, where shared clothing and bedding should be avoided and washed thoroughly). The infection itself is not communicable through normal daily contact.
Your risk comes from the same source as theirs: the animal or insect vector. If a cat in the home transmitted the infection, other household members with cat scratches or flea exposure face the same risk independently. Flea control for pets, prompt cleaning of cat scratches, and avoiding rough play with kittens are the most effective prevention steps.