01OverviewDefinition, clinical context and the essential points that orientate the chapter.
Reactive arthritis is an inflammatory spondyloarthritis triggered by infection outside the joint. Establish precise timing, organism exposure, antibiotics, sexual contacts and public-health risk. Examine joints, entheses, digits, skin, nails, mouth, genital or urinary symptoms, eyes and spine. The historical urethritis–arthritis–conjunctivitis triad is insensitive and should not be required for diagnosis.
There is no single diagnostic test. FBC, CRP and ESR support severity but may be normal. Obtain NAAT for chlamydia and gonorrhoea from the appropriate sites and stool testing when ongoing diarrhoea or public-health context justifies it. HLA-B27 is not a diagnostic infection test. Joint aspiration is essential when infection or crystals are possible; reactive synovial fluid is inflammatory but culture-negative.
Management separates infection from inflammation. Treat active sexually transmitted infection using current BASHH or local sexual-health guidance. Advise abstinence from sexual intercourse, including oral sex, until treatment is completed and symptoms have resolved; discuss and document partner notification, and offer screening for other STIs including HIV and indicated hepatitis B screening and vaccination. Do not prescribe prolonged antibiotics solely for arthritis after cleared enteric infection. Consider local corticosteroid only after sepsis is excluded and never inject tendon substance.
Most episodes improve over months, but recurrence or persistence requires rheumatology assessment for DMARD treatment and reclassification within spondyloarthritis. Monitor eye symptoms, axial pain, function and medication harms. Address work, mobility and sexual-health confidentiality in a non-stigmatising manner.
Key points
- Reactive arthritis usually begins days to several weeks after genitourinary or enteric infection and commonly causes asymmetric lower-limb oligoarthritis, enthesitis or dactylitis.
- Ask about diarrhoea, dysuria, discharge, pelvic symptoms, sexual exposure, conjunctivitis, uveitis, oral lesions, keratoderma and heel pain without relying on the obsolete complete triad.
- A trigger may have been mild or resolved; request infection tests according to timing, symptoms and sexual-health or public-health implications.
- Aspirate a hot effusion for culture and crystals because septic arthritis, gonococcal infection and gout remain critical alternatives.
- Treat confirmed active chlamydial or other infection according to current antimicrobial and partner-management guidance; antibiotics do not reliably cure established sterile arthritis after cleared enteric infection.
- NSAIDs are commonly used for articular symptoms when safe. Intra-articular corticosteroid may help a selected joint only after infection is excluded; peri-entheseal injection needs an experienced clinician and must not enter tendon substance, particularly at the Achilles tendon.
- Persistent peripheral arthritis warrants rheumatology reassessment. A conventional DMARD may be considered after infection is excluded, but evidence is limited and it should not be assumed to treat axial disease.
- Provide sexual-health counselling, notification and retesting as indicated, and review for a continuing axial or peripheral spondyloarthritis phenotype.
02AetiologyUnderlying causes, associations and risk factors, with why each one matters.
Genitourinary infection
Chlamydia trachomatis is an important trigger, often with mild or unrecognised urethral or cervical symptoms before arthritis begins.
Enteric infection
Salmonella, Shigella, Campylobacter and Yersinia can trigger arthritis after diarrhoeal illness through immune responses rather than viable organisms within the joint.
Host susceptibility
HLA-B27 and other immune factors influence severity and persistence, but testing does not confirm the diagnosis or identify the triggering organism.
03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.
- 1Post-infectious immune activation
Microbial antigens and mucosal immune signals activate inflammatory pathways after the original infection, producing sterile synovial and entheseal inflammation.
- 2Spondyloarthritis tissue pattern
Inflammation favours lower-limb joints, entheses, whole digits, sacroiliac structures, eye and mucocutaneous sites rather than a purely symmetrical small-joint pattern.
- 3Persistence in susceptible hosts
Ongoing antigen exposure or dysregulated immunity can sustain symptoms and evolve into chronic peripheral or axial spondyloarthritis in a minority.
04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.
Asymmetric knee, ankle or foot inflammation beginning after diarrhoea or genitourinary symptoms is characteristic, especially with heel enthesitis or dactylitis.
Oral lesions, circinate balanitis, keratoderma and conjunctival symptoms support reactive arthritis but may be absent or subtle.
Eye pain, photophobia, redness or blurred vision requires same-day ophthalmology rather than treatment as uncomplicated conjunctivitis.
Migratory pain, tenosynovitis, sparse pustules and sexual exposure requires urgent multi-site microbiology and antimicrobial assessment.
Symptoms beyond the expected episode, inflammatory back pain or recurrent enthesitis suggests a persistent axial or peripheral disease requiring specialist review.
05InvestigationsWhat to request, why it matters and how to interpret it.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
Synovial-fluid culture and crystalsFirst step - Why
- Exclude septic and crystal arthritis in an acutely inflamed accessible joint.
- Interpretation and limitations
- Sterile inflammatory fluid supports but does not prove reactive arthritis; prior antibiotics reduce culture yield and blood cultures may still identify infection.
- 02
Chlamydia and gonorrhoea NAAT - Why
- Identify a treatable active genitourinary trigger and support partner management.
- Interpretation and limitations
- Select urine and anatomical sites from exposure and sexual-health guidance; negative testing after delay does not exclude a prior cleared trigger.
- 03
Stool microbiology - Why
- Identify ongoing enteric infection when diarrhoea, outbreak or public-health implications persist.
- Interpretation and limitations
- A negative late sample does not exclude a preceding trigger, and a positive result does not remove the need to culture a hot joint.
- 04
FBC, CRP, ESR, renal and liver profile - Why
- Assess systemic inflammation, alternative infection and baseline safety for anti-inflammatory or DMARD treatment.
- Interpretation and limitations
- Markers are nonspecific and normal results cannot exclude reactive or septic arthritis; organ abnormalities redirect urgency.
- 05
Targeted imaging - Why
- Assess structural damage, persistent enthesitis or axial disease when symptoms do not resolve.
- Interpretation and limitations
- Early radiography may be normal; ultrasound or MRI supports selected questions but does not identify the infectious trigger.
06Differential diagnosisRealistic alternatives and the features that help distinguish them.
Septic arthritis
Fever, bacteraemia risk or one markedly hot restricted joint requires urgent aspiration because a preceding infection does not prove reactive disease.
Disseminated gonococcal infection
Migratory arthritis, tenosynovitis, skin lesions and sexual exposure require site-specific testing and antimicrobial treatment rather than a sterile-arthritis assumption.
Psoriatic or enteropathic arthritis
Psoriasis, nail disease, established inflammatory bowel disease or recurrent axial symptoms may indicate another spondyloarthritis phenotype.
Crystal arthritis
Abrupt monoarthritis, tophi or CPP risk requires synovial crystal analysis, with simultaneous culture when infection remains possible.
07ManagementImmediate care, first-line treatment, alternatives and escalation.
01Acute post-infectious arthritisCulture the joint and identify active infectionFirst stepNew lower-limb arthritis follows diarrhoea or genitourinary symptoms without haemodynamic instability.+
- 1Take sexual, gastrointestinal and medicine history, examine joint, skin, eye and entheses, and aspirate any significantly hot effusion for culture and crystals.
- 2Request site-appropriate chlamydia and gonorrhoea NAAT and stool tests when indicated, while assessing sepsis and disseminated infection risk.
- 3Treat confirmed active infection through antimicrobial and partner pathways and use comorbidity-adjusted anti-inflammatory care for sterile symptoms.
02Persistent inflammationReassess the phenotype before DMARD treatmentArthritis, enthesitis or axial symptoms remain function-limiting beyond the expected self-limited course.+
- 1Confirm that infection was adequately tested and treated, re-examine for psoriasis, bowel disease, uveitis and axial spondyloarthritis and assess adherence and function.
- 2Refer to rheumatology. After infection is excluded, a conventional DMARD may be considered for persistent peripheral arthritis, but evidence is limited and conventional treatment should not be assumed to control axial disease.
- 3Use specialist targeted therapy only for established ongoing spondyloarthritis meeting disease-specific criteria, with vaccination and infection precautions.
03Painful red eyeProtect sightReactive-arthritis symptoms accompany eye pain, photophobia, reduced vision or ciliary redness.+
- 1Arrange same-day ophthalmic assessment and do not assume all ocular redness is benign conjunctivitis.
- 2Record visual symptoms and current immunosuppression and coordinate infection or STI information relevant to the ophthalmic differential.
- 3Follow ophthalmic treatment and recurrence advice while rheumatology controls the associated systemic inflammatory disease.
Key medicines and prescribing safety2 treatments · regimens, roles and cautions+
Naproxen
Common adult dosing is 250–500 mg orally twice daily with food for a reviewed short course when clinically suitable.Assess GI ulcer or bleeding, renal, cardiovascular and anticoagulant risk; use the lowest effective dose for the shortest time with gastroprotection when indicated. Avoid from 20 weeks of pregnancy unless clinically necessary and do not use from 28 weeks; follow current MHRA and product advice.
Doxycycline for uncomplicated chlamydia
100 mg orally twice daily for 7 days is the usual adult regimen, subject to current sexual-health guidance and patient factors.Doxycycline is contraindicated for routine treatment in pregnancy; the 2026 BASHH guideline permits it only when the full course finishes before 15 weeks and no suitable alternative exists. Check allergy, oesophageal irritation, photosensitivity and interactions; provide partner-notification and STI-screening support.
08ComplicationsImportant consequences, why they occur and why they matter clinically.
Chronic spondyloarthritis
Persistent arthritis, enthesitis or inflammatory back pain can evolve beyond the initial post-infectious episode and require disease-modifying specialist care.
Anterior uveitis
Painful photophobic ocular inflammation can recur and threaten vision without prompt slit-lamp assessment and topical treatment.
Functional and sexual-health consequences
Pain, reduced mobility, stigma, untreated infection and partner reinfection can prolong illness and create avoidable psychosocial harm.
09Monitoring and follow-upTreatment response, safety checks and longer-term review.
- Review joint count, enthesitis, dactylitis, axial symptoms, function and eye symptoms over the following weeks.
- For people under 25, arrange repeat chlamydia testing two to six months after treatment. Arrange test of cure no earlier than three weeks after treatment in pregnancy or when adherence or persistent symptoms warrants it.
- Monitor renal, gastrointestinal and cardiovascular safety during NSAID treatment.
- Reopen septic arthritis when fever, one-joint deterioration or poor response occurs despite an initial reactive diagnosis.
- Refer persistent or recurrent disease for chronic spondyloarthritis assessment and DMARD monitoring.
10Special situationsVariants, exceptions and circumstances that change the usual approach.
The trigger may be silent
Chlamydial infection can be asymptomatic, so a sensitive and nonjudgmental sexual history matters even when urethritis is absent.
The triad is optional
Arthritis does not need simultaneous urethritis and conjunctivitis to qualify; requiring all three misses many cases.
Antibiotics have a defined target
They treat active infection and transmission, while established sterile inflammation requires its own anti-inflammatory and rheumatological plan.
HLA-B27 is not confirmation
It modifies susceptibility and persistence risk but neither identifies the organism nor proves the syndrome.
Uveitis differs from conjunctivitis
Pain, photophobia and visual change are warning features that require urgent slit-lamp assessment.
11Common pitfallsFrequent interpretation and management errors.
- 01
Diagnosing reactive arthritis without aspirating a suspicious hot joint.
- 02
Requiring the complete historical triad before considering the diagnosis.
- 03
Using prolonged antibiotics for sterile arthritis after a cleared enteric infection.
- 04
Failing to test and manage partners after confirmed chlamydia.
- 05
Treating painful photophobic eye as simple conjunctivitis.