Case History
A 10 year old female presented to the pediatric emergency department (ED) with a chief complaint of persistent fever and chills for the past 10 days. Her mother reported the fevers reached up to 103°F and temporarily would respond to ibuprofen. She also noted a decrease in the patient’s appetite, tiredness and a bumpy rash on her truck and extremities. In the ED, she was clinically stable but her temperature reached a max of 104.7°F. On physical examination, shotty cervical lymphadenopathy was noted and there was no appreciable enlargement of the liver or spleen. Initial laboratory testing showed a white blood cell count of 10.6 TH/cm2 (normal range: 4.3-11.4 TH/cm2) and elevated acute phase proteins (ESR 45 mm/HR and CRP 2.6 mg/dL). Blood cultures were collected and the patient was started on ceftriaxone. Pediatric infectious disease was consulted and a thorough infectious work up was completed.
Laboratory Identification
- Rapid influenza antigen test: Negative
- Rapid Group A Strep antigen test: Negative
- Rapid Monospot: Negative
- HIV antigen/antibody (4th generation) test: Negative
- Legionella urinary antigen: Negative
- Histoplasma urinary antigen: Negative
- Antinuclear antibody: Negative
- Rheumatoid factor: Negative
- Urine culture: Negative
- Blood cultures: Negative
- Bartonella henselae IgM: ≥1:20 (normal <1:20)
- Bartonella henselae IgG: ≥1:1024 (normal <1:128)
Infectious disease and rheumatologic work ups, as listed above, were negative with the exception of a positive IgM and IgG serologic testing for Bartonella henselae, with the results suggesting a recent infection based on the elevated titers. Upon further questioning, the family did have many outdoor cats and dogs; however, the child denied any recent bites or scratches.
Discussion
Bartonella henselae is a facultative, Gram negative coccobacillary rod that is the causative agent of cat scratch disease and bacillary angiomatosis. The main reservoir for B. henselae is cats and the disease is spread from cat to cat via the cat flea. Feral cats, outdoor cats and young kittens, especially those living in hot, humid environments where fleas are plentiful, are more likely to be infected and spread the disease to humans via infective flea feces during a scratch or bite from the cat.
The incubation period for B. henselae ranges from 1-3 weeks and the majority of patients present with systemic symptoms including fever, chills, malaise, anorexia and headache. In addition, painful lymphadenopathy, on the side of the body where the scratch occurred (most common upper extremity), can be present in the epitrochlear, axillary and cervical regions. Less frequently, B. henselae causing bacillary angiomatosis can result in the proliferation of vessels in organs (liver and spleen). Though rare, encephalopathy and endocarditis due to B. henselae are the most severe manifestations of disease.
In the microbiology laboratory, the diagnosis of B. henselae is challenging due to the fact it is slow growing, highly hemin dependent and requires high humidity conditions for growth. The organism will grow on chocolate and heart infusion agars containing 5% fresh rabbit blood. Plates should be incubated at 35°C with 5% CO2 with high humidity for at least 4 weeks. Colonies are irregular and off-white in color and B. henselae is negative for both catalase & oxidase and asaccharolytic.
Due to the identification difficulties with culture, serologic testing is the main methodology for the diagnosis of B. henselae. Enzyme linked immunosorbent assays (ELISA) are relatively easy to perform and provides good results, although the provider should be aware of the sensitivity of the particular platform, the fact that cross reactivity with other Bartonella spp. can occur and seronegative infections can sometimes occur. Warthin-Starry silver stain on fixed tissue sections from lymph nodes and other organs can be helpful as well; however, it is relatively insensitive and not highly specific.
With regards to treatment, there are no agreed upon breakpoints for B. henselae published by CLSI or EUCAST. Microdilution or Etests can be used for testing and isolates have been susceptible to many antibiotics. In general, for cat scratch disease, it does not respond to antibiotic therapy and there is only a minimal benefit of antimicrobial agents. In the case of our patient, she was switched from ceftriaxone to a five day course of azithromycin with a gradual improvement of her fever curve. She was scheduled to follow up with pediatric infectious disease in 2-3 weeks.
-Lisa Stempak, MD, is an Assistant Professor of Pathology at the University of Mississippi Medical Center in Jackson, MS. She is certified by the American Board of Pathology in Anatomic and Clinical Pathology as well as Medical Microbiology. She is the Director of Clinical Pathology as well as the Microbiology and Serology Laboratories. Her interests include infectious disease histology, process and quality improvement and resident education.
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