Clinical guide needed to improve management of cat-scratch disease

Certain concerns have been raised regarding the serologic diagnosis of cat-scratch disease (CSD), which include the use of low titres for positivity, incomplete diagnostic evaluation, and the lack of convalescent serologic testing, reveals a study.

“We propose a clinical guide to assist in managing suspected cases of CSD,” the authors said.

A retrospective chart review of immunocompetent paediatric patients was carried out at the Hospital for Sick Children in Toronto, Canada, spanning a period of 11 years. In total, 154 cases were included with serologic titres ≥1:128. These were further divided into the following groups: group 1=1:128; group 2=1:256; and group 3 ≥1:512.

The authors evaluated cases within groups with respect to cat contact, clinical presentation, further testing, and final diagnosis.

Among patients with a titre of 1:128, one-third had an alternative diagnosis. Most patients with a titre of 1:128 or 1:256 did not undergo convalescent serologic testing. Only one case within these two groups had a fourfold rise in the convalescent titre.

Furthermore, there was a trend of decreasing number of patients with alternative diagnoses (p=0.03) and increasing number of patients presenting with regional lymphadenopathy (p=0.07) which correlated with higher titres in group 3 compared with group 1.

Bartonella henselae serology is commonly used to diagnose CSD, with titres above a threshold for positivity suggesting either a recent or remote infection. A fourfold increase in the convalescent titre in some cases could confirm a recent infection.

“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,” the authors said.