Background: Bartonella henselae serology is commonly used to diagnose cat-scratch disease (CSD). Titers above a threshold for positivity suggest either a recent or remote infection. Recent infection can be confirmed by a 4-fold rise in the convalescent titer in some cases. Many atypical presentations attributed to CSD utilize a low threshold for positivity without supportive evidence from convalescent sera or supplemental testing, raising a concern for the overdiagnosis of CSD.
Methods: We conducted a retrospective chart review of immunocompetent pediatric patients at the Hospital for Sick Children, Toronto, spanning an 11-year period. A total of 154 cases were included with serologic titers ≥1:128. These were divided into 3 groups: group 1 = 1:128, group 2 = 1:256, and group 3 ≥ 1:512. Cases within groups were evaluated with respect to cat contact, clinical presentation, further testing, and final diagnosis.
Results: One-third of patients with a titer of 1:128 had an alternative diagnosis. Most cases with a titer of 1:128 or 1:256 did not have convalescent serologic testing performed. Within these 2 groups, only 1 case had a 4-fold rise in the convalescent titer. A trend of decreasing number of cases with alternative diagnoses (P = 0.03) and increasing number of cases presenting with regional lymphadenopathy (P = 0.07) was associated with higher titers in group 3 compared with group 1.
Conclusion: Concerns about the serologic diagnosis of CSD include the use of low titers for positivity, incomplete diagnostic evaluation, and the lack of convalescent serologic testing. We propose a clinical guide to assist in managing suspected cases of CSD.