Cat scratch disease is a zoonotic infection caused by Bartonella henselae, transmitted primarily through cat scratches or bites. It is the most common cause of chronic regional lymphadenopathy in children and adolescents, and is typically self-limited in immunocompetent patients. [1-2]
1. History
- Exposure: Ask about cat or kitten contact — scratches, bites, or licks to broken skin. ~92% of patients report feline exposure. Kittens (<1 year) are higher-risk vectors than adult cats. [2-3]
- Inoculation site: A papule or pustule develops 3–30 days after the scratch/bite at the wound site. [1]
- Lymphadenopathy onset: Regional lymph nodes enlarge approximately 3 weeks after inoculation, typically proximal to the scratch site. [1]
- Timing/seasonality: Peak incidence in late summer and fall (August–September). [3]
- Symptom characterization: Tender, unilateral lymphadenopathy (axillary, cervical, epitrochlear, inguinal); low-grade fever; malaise; fatigue; headache. [2][4]
- Important negatives: Weight loss, night sweats, travel history, TB exposure, immunosuppression status, tick bites.
2. Alarm Features
- High fever (>39°C) persisting >2 weeks — consider disseminated disease [4-5]
- Seizures or altered mental status — CSD encephalitis occurs in ~0.5% of cases; 68% present with seizures, including status epilepticus [6]
- Visual changes — neuroretinitis or Parinaud oculoglandular syndrome [7]
- Abdominal pain with hepatosplenomegaly — hepatosplenic microabscesses [3][8]
- Bone pain — osteomyelitis [5]
- Immunocompromised patient (HIV/AIDS, transplant, biologics) — risk of bacillary angiomatosis, peliosis hepatis, bacteremia, and endocarditis [1][9-10]
- Rapidly enlarging or fixed lymph node — must exclude lymphoma
3. Medications
- First-line (IDSA recommendation): Azithromycin [1]
- ≥45 kg: 500 mg PO day 1, then 250 mg PO daily × 4 days
- <45 kg: 10 mg/kg PO day 1, then 5 mg/kg PO daily × 4 days
- Alternative: TMP/SMX has shown comparable effectiveness in pediatric studies [11]
- Disseminated/severe disease: Doxycycline 100 mg BID ± rifampin 300 mg BID for 2 weeks to 2 months [10]
- CNS involvement: Doxycycline ± rifampin [10]
- Endocarditis: Doxycycline + rifampin × 6 weeks, then doxycycline ≥3 months [10]
- Bacillary angiomatosis (immunocompromised): Erythromycin 500 mg QID or doxycycline 100 mg BID for 2 weeks to 2 months; HIV patients may require lifelong therapy [1][10]
- Contraindications: Doxycycline avoided in children <8 years for prolonged courses; avoid first/second-generation cephalosporins (lack efficacy against Bartonella) [10]
4. Diet
- No specific dietary triggers or restrictions.
- Ensure adequate hydration during febrile illness.
- No long-term dietary management required.
5. Review of Systems
- Constitutional: Fever, malaise, fatigue, anorexia, weight loss
- HEENT: Visual changes (neuroretinitis), conjunctival injection (Parinaud syndrome), headache
- Neurologic: Seizures, confusion, focal deficits (encephalitis)
- GI: Abdominal pain, nausea (hepatosplenic involvement)
- MSK: Bone pain (osteomyelitis)
- Skin: Rash, papule/pustule at inoculation site, erythema nodosum
- Cardiac: Dyspnea, new murmur (endocarditis — rare)
6. Collateral History and Family History
- Pet ownership: Number and age of cats, flea infestation status, indoor vs. outdoor cats
- Household contacts: Other family members with similar symptoms
- Occupational exposure: Veterinarians, animal shelter workers
- Family history is generally not contributory, though immunodeficiency syndromes should be explored if disseminated disease is present
7. Risk Factors
- Cat ownership, especially kittens <1 year old [2]
- Cat flea infestation — fleas transmit B. henselae between cats [2]
- Immunosuppression: HIV/AIDS, organ transplant, biologic therapy (e.g., abatacept) [9-10]
- Age: Peak incidence in children aged 5–14 years [3]
- Season: Late summer/early fall [3]
- Dog exposure: Reported in ~22% of cases, though less common than feline exposure [3]
8. Differential Diagnosis
- Lymphoma — fixed, non-tender, progressive lymphadenopathy; B symptoms
- Mycobacterial infection (TB or NTM) — chronic lymphadenopathy, granulomas, exposure history
- Toxoplasmosis — cat exposure overlap; cervical lymphadenopathy; serology differentiates
- EBV/CMV mononucleosis — generalized lymphadenopathy, pharyngitis, atypical lymphocytes
- Tularemia — ulceroglandular form mimics CSD; rabbit/tick exposure
- Sporotrichosis — lymphocutaneous pattern after thorn/soil exposure
- Bacterial lymphadenitis (Staph/Strep) — more acute, erythematous, fluctuant
- Kikuchi disease — self-limited necrotizing lymphadenitis, young women
- Sarcoidosis — bilateral hilar lymphadenopathy, non-caseating granulomas
9. Past Medical History
- Prior episodes of CSD (reinfection is possible but uncommon)
- Immunosuppressive conditions or medications — critical for risk stratification [9-10]
- Splenectomy (risk of overwhelming infection)
- Valvular heart disease (endocarditis risk)
- Prior lymph node biopsies
10. Physical Exam
- Inoculation site: Look for a papule, pustule, or healing scratch on the hand, arm, or face [1][12]
- Lymphadenopathy: Tender, unilateral, regional; most commonly axillary, cervical, or epitrochlear. Nodes may be 1–5 cm; ~10% suppurate [1]
- Vital signs: Low-grade fever common; high fever suggests disseminated disease
- Abdomen: Hepatosplenomegaly in disseminated cases [3][8]
- Eyes: Fundoscopy for neuroretinitis (macular star pattern), conjunctival granuloma (Parinaud syndrome)
- Skin: Erythema nodosum (rare), bacillary angiomatosis lesions in immunocompromised (red papules or subcutaneous nodules) [1]
- Neurologic exam: Mental status, focal deficits if encephalitis suspected [6]
11. Lab Studies
- Serology (IFA): IgM and IgG to B. henselae — IgG titer ≥1:256 is highly suggestive. Cross-reactivity with B. quintana and other organisms exists. [1-2][13]
- PCR: Can be performed on lymph node aspirate, biopsy, or blood; higher sensitivity than serology alone [13-14]
- CBC: Usually normal; mild leukocytosis possible [4]
- ESR/CRP: Elevated in ~47% and ~21% of cases, respectively [4]
- LFTs: Elevated transaminases in hepatosplenic disease [8][15]
- Blood cultures: Typically negative (fastidious organism) [1]
- To rule out dangerous conditions: LDH, uric acid, peripheral smear (if lymphoma concern); monospot/EBV panel; HIV testing in at-risk patients
12. Imaging
- Ultrasound: First-line for evaluating lymphadenopathy — typically shows enlarged, hypoechoic nodes; may show suppuration
- CT abdomen: Indicated if hepatosplenic involvement suspected — look for hepatic/splenic microabscesses [3][8][16]
- MRI: For CNS involvement (encephalitis) or osteomyelitis; neuroimaging is normal in ~79% of CSD encephalitis cases [6]
- Imaging is unnecessary in classic, uncomplicated CSD with typical lymphadenopathy and clear exposure history
13. Special Tests
- Warthin-Starry silver stain: Demonstrates bacilli in lymph node biopsy tissue; cannot differentiate Bartonella species [1]
- Histopathology: Stellate caseating granulomas, microabscesses, follicular hyperplasia [12]
- mNGS (metagenomic next-generation sequencing): Emerging diagnostic tool, particularly useful when conventional methods are inconclusive or biopsy is refused [14-15]
- Lymph node aspiration: Both diagnostic (send for PCR, culture, histology) and therapeutic if suppurative
- Combined serology + PCR increases diagnostic yield from ~28% to ~44% [13]
14. ECG
- Not routinely indicated in typical CSD
- Obtain ECG if endocarditis is suspected (new murmur, prolonged bacteremia, immunocompromised patient)
- Bartonella endocarditis is culture-negative; echocardiography (TTE/TEE) is more relevant than ECG in this setting
15. Assessment
- Typical presentation: Self-limited regional lymphadenopathy in a child or young adult with cat exposure, preceded by an inoculation papule. Resolves within 1–6 months without treatment. [1-2]
- Atypical/disseminated disease: Occurs in 5–20% of cases; includes hepatosplenic, ocular, neurologic, and osteoarticular manifestations. Atypical CSD carries an 8.8× increased risk of hospitalization. [7]
- Severity stratification:
- Mild: Isolated lymphadenopathy, no systemic symptoms → outpatient management
- Moderate: Persistent fever, large/suppurative nodes → antibiotics, close follow-up
- Severe: Encephalitis, hepatosplenic disease, endocarditis, immunocompromised → admission, combination antibiotics
16. Treatment Plan
- Mild/uncomplicated CSD: Supportive care is often sufficient. Azithromycin may speed lymph node regression. [1]
- Suppurative nodes: Needle aspiration for symptom relief (preferred over incision and drainage to avoid fistula formation)
- Disseminated/severe disease in immunocompetent patients: Azithromycin + rifampin, or doxycycline + rifampin for 2 weeks to 2 months [10][17]
- Immunocompromised patients: Doxycycline 100 mg BID or erythromycin 500 mg QID for ≥3 months; HIV patients with relapse may need long-term suppressive therapy [10]
- Encephalitis: Supportive care is primary; antibiotic and corticosteroid use remains under investigation. Prognosis is generally favorable, though recovery may take months and ~42% report persistent cognitive complaints. [6]
- Analgesics/antipyretics: NSAIDs or acetaminophen for pain and fever
17. Disposition
- Discharge criteria: Uncomplicated lymphadenopathy, no systemic toxicity, tolerating PO, reliable follow-up
- Admission criteria:
- Encephalitis/seizures/status epilepticus [6]
- Hepatosplenic disease with significant abdominal pain or hemodynamic concern
- Endocarditis
- Immunocompromised with disseminated disease [9-10]
- Inability to tolerate oral medications
- Observation: Consider for patients with high fever, large suppurative nodes requiring aspiration, or diagnostic uncertainty (lymphoma workup)
- Specialist consultation: Infectious disease (disseminated/atypical cases), ophthalmology (neuroretinitis), neurology (encephalitis), surgery (biopsy if malignancy concern)
18. Follow Up / Return Precautions
- Follow-up timing: 2–4 weeks for uncomplicated cases to reassess lymphadenopathy
- Expected course: Lymphadenopathy resolves over 1–6 months; some nodes may persist longer [1]
- Return precautions — advise return for:
- New or worsening fever
- Rapidly enlarging or new lymph nodes
- Visual changes
- Seizures, confusion, or severe headache
- Abdominal pain
- Skin lesions (especially in immunocompromised)
- Patient counseling:
- CSD is not transmitted person-to-person
- Flea control on cats reduces transmission risk
- Avoid rough play with kittens; wash scratches/bites promptly
- No need to rehome the cat [2]
References
1. Practice Guidelines for the Diagnosis and Management of Skin and Soft Tissue Infections: 2014 Update by the Infectious Diseases Society of America. — Stevens DL, Bisno AL, Chambers HF, et al. Clinical Infectious Diseases : An Official Publication of the Infectious Diseases Society of America. 2014.
2. Cat-Scratch Disease. — Klotz SA, Ianas V, Elliott SP. American Family Physician. 2011.
3. Cat Scratch Disease: 9 Years of Experience at a Pediatric Center. — Amin O, Rostad CA, Gonzalez M, et al. Open Forum Infectious Diseases. 2022.
4. A Retrospective Analysis of Systemic Bartonella Henselae Infection in Children. — Stroescu RF, Chisavu F, Steflea RM, et al. Microorganisms. 2024.
5. Unusual Presentation of Cat Scratch Disease: Case Report. — Aslan Tuncay S, Akkoc G, Yilmaz S, et al. European Journal of Clinical Microbiology & Infectious Diseases : Official Publication of the European Society of Clinical Microbiology. 2024.
6. Cat Scratch Disease Encephalitis: New Insights Into Rate, Clinical Features, and Long-Term Outcomes. — Yakubovsky M, Kadar L, Katchman E, et al. International Journal of Infectious Diseases : IJID : Official Publication of the International Society for Infectious Diseases. 2026.
7. Atypical Manifestations of Cat-Scratch Disease, United States, 2005-2014. — Nawrocki CC, Max RJ, Marzec NS, Nelson CA. Emerging Infectious Diseases. 2020.
8. Hepatosplenic Cat Scratch Disease in Immunocompetent Adults: Report of 3 Cases and Review of the Literature. — García JC, Núñez MJ, Castro B, et al. Medicine. 2014.
9. Disseminated Cat-Scratch Disease During Abatacept Therapy for Rheumatoid Arthritis in an Older Patient: A Case Report and Review of the Literature. — Saito H, Takahashi Y, Tsuge S, et al. Journal of Infection and Chemotherapy : Official Journal of the Japan Society of Chemotherapy. 2025.
10. Guidelines for the Prevention and Treatment of Opportunistic Infections in Adults and Adolescents With HIV. — Constance Benson, John Brooks, Shireesha Dhanireddy, et al Infectious Diseases Society of America; Office of AIDS Research Advisory Council (2025). 2025.
11. Effectiveness of Antibiotic Therapy in Pediatric Patients With Cat Scratch Disease. — Shorbatli LA, Koranyi KI, Nahata MC. International Journal of Clinical Pharmacy. 2018.
12. Cat Scratch Disease, Bacillary Angiomatosis, and Other Infections Due to Rochalimaea. — Adal KA, Cockerell CJ, Petri WA. The New England Journal of Medicine. 1994.
13. Serological and Molecular Detection of Bartonella Henselae in Specimens From Patients With Suspected Cat Scratch Disease in Italy: A Comparative Study. — Allizond V, Costa C, Sidoti F, et al. PloS One. 2019.
14. A Case Report of Diagnosis of Cat-Scratch Disease Using Metagenomic Next-Generation Sequencing. — Zhou T, Zheng Y, Zhang H, Liu Y. Frontiers in Cellular and Infection Microbiology. 2023.
15. Diagnosis of Cat-Scratch Disease by Metagenomic Next-Generation Sequencing. — Yue Y, Kang YJ, Wang H, et al. Vector Borne and Zoonotic Diseases. 2026.
16. Cat Scratch Disease. Report of a Case With Hepatic Lesions and a Brief Review of the Literature. — Rocco VK, Roman RJ, Eigenbrodt EH. Gastroenterology. 1985.
17. Clinical and Epidemiological Characteristics of Cat Scratch Disease in Children From Southwestern China: A Retrospective Analysis of mNGS-confirmed Cases. — Lai SY, Chang L, Duan JX, et al. Frontiers in Public Health. 2025.