Delayed diagnosis of cat-scratch disease reported in Portugal

Cat-scratch disease is a well-recognised zoonosis, primarily caused by Bartonella henselae, with a broad clinical spectrum in which atypical manifestations may delay diagnosis. A study published on 8 September 2026 in the European Journal of Clinical Microbiology & Infectious Diseases characterised the clinical and epidemiological profile of the disease at a Portuguese tertiary care centre and evaluated the role of molecular and serological methods as complementary tools.

The retrospective cohort included all patients with laboratory-confirmed diagnosis at Unidade Local de Saúde de São João, in Porto, between 2010 and 2025: 39 people, median age 15 years, 53.8% of them paediatric. Cat exposure was reported in 94.9% of cases; information on flea infestation and preventive measures in companion animals was unavailable in the records. Systemic presentations occurred in 43.6% of patients, and the great majority of those (94.1%) were immunocompetent.

Among PCR-positive specimens that could be sequenced, all were identified as B. henselae. PCR positivity was much higher in lymph node tissue (79.2%) than in blood (15.8%). The median time from symptom onset to diagnosis was 52.5 days. At diagnosis, serology was positive for IgG in 76.0% of patients and for IgM in 28.0%. Azithromycin monotherapy was the most frequently used treatment for typical disease (81.8%), while combination therapy predominated in systemic cases (76.5%); clinical resolution after a single course of treatment was achieved in 74.4% of patients.

The authors conclude that the disease frequently presented with systemic involvement, including in immunocompetent patients, and that the prolonged interval to diagnosis highlights the need for greater clinical awareness and improved access to serological and molecular diagnostics. Given the high frequency of cat exposure, they propose that One Health strategies focused on responsible pet ownership, regular flea control and veterinary follow-up may help reduce Bartonella transmission and the burden of the disease.

A series published in 2022 in Open Forum Infectious Diseases gathered 304 children diagnosed at a tertiary paediatric hospital system in Atlanta, Georgia, between 2010 and 2018. The largest proportion of diagnoses was made in August (13.5%) and September (15.5%). Median age was 8.1 years; 92.4% of children with a documented history reported feline exposure and 22% canine exposure. Lymphadenopathy was present on physical examination in the majority (78.8%), but atypical presentations lacking lymphadenopathy were also common (20.7%); among children with imaging, 36.4% had splenomegaly and 38.1% splenic or hepatic microabscesses. Veterinary data from the state, reviewed in the same study, showed a Bartonella seroprevalence of 8.2%, all in dogs.

Cats are the primary reservoir host of B. henselae. A study published in 2021 in Pathogens, with shelter and client-owned cats, found seroreactivity of 78% in serum by immunofluorescence, in both the in-house and the commercial assay, and 56.8% in oral fluid, with only moderate agreement between the two specimens (kappa 0.434); the authors concluded that oral fluid antibodies are of limited utility for epidemiological or diagnostic purposes.

For the veterinarian, the point of contact with these three papers is flea control: it is the vector between cats, and the Portuguese study notes that information on fleas and prevention in patients' animals was simply absent from the medical records. Recording and advising on that in the veterinary clinic is a direct contribution to surveillance of a zoonosis that, in the Portuguese data, took almost two months to diagnose.