Latent infection screening before immunosuppression

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Latent organisms persist because normal immunity contains rather than eradicates them. Mycobacterium tuberculosis survives within granulomatous lesions; hepatitis B covalently closed circular DNA remains in hepatocytes after HBsAg clearance; Strongyloides maintains lifelong autoinfection; herpesviruses persist in neural or haematopoietic reservoirs. Immunosuppressive treatments disrupt different containment systems, so a useful screen is matched to the planned mechanism and the person's epidemiology.

Universal core assessment commonly includes TB, hepatitis B and C and HIV, with baseline FBC, renal and liver profiles and vaccination review. Additional tests are selective: Strongyloides after endemic soil exposure, VZV IgG when history is uncertain, and CMV, EBV or toxoplasma serology for transplantation or other defined protocols. Indiscriminate panels create false positives and do not replace a detailed history.

The result must lead to an action and owner. Negative testing may be unreliable during immune suppression; positive antibody may mean vaccine immunity, resolved infection or active replication depending on the marker. Preventive treatment introduces hepatic toxicity and major interactions, while delaying cancer, vasculitis or transplant therapy also causes harm. A documented plan should state whether immune treatment waits, begins after a minimum preventive interval or proceeds with simultaneous prophylaxis and surveillance.

Key points

Screen before the first immunosuppressive dose whenever possible, because corticosteroids and targeted agents reduce test sensitivity, accelerate reactivation and narrow vaccination options.
Begin with birthplace, residence and travel, TB contact and treatment, blood and sexual exposure, previous hepatitis, recurrent infection, VZV history, vaccines, prior biologics and planned drug mechanism.
TB assessment combines symptom review, examination, chest radiography and IGRA, with TST added when appropriate; no single test is a gold standard for latent infection.
A positive IGRA or TST indicates immune sensitisation, not proof of latency: exclude active tuberculosis clinically, radiologically and microbiologically before preventive treatment.
Hepatitis B screening requires HBsAg, total anti-HBc and anti-HBs; if HBsAg or anti-HBc is positive, obtain HBV DNA and specialist risk stratification.
Check hepatitis C antibody with confirmatory RNA after a reactive result and offer HIV antigen-antibody testing according to the treatment pathway and current national practice.
Use exposure-driven Strongyloides assessment before corticosteroids or major immunosuppression and establish VZV immunity and vaccination needs before live vaccines become unsafe.
A screen is not a one-off guarantee: new exposure, travel, symptoms or a changed immune regimen requires renewed risk assessment even when baseline tests were negative.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Contained mycobacterial infection

Viable M. tuberculosis may persist after asymptomatic exposure within granulomatous lesions, with lifetime reactivation risk amplified by TNF and cellular immune suppression.

Persistent hepatotropic viruses

HBV nuclear templates survive after apparent serological recovery, while unrecognised chronic HBV or HCV replication may accelerate during immune treatment.

Lifelong parasite autoinfection

Strongyloides larvae recycle through gut and lungs for decades after endemic exposure and can multiply explosively when corticosteroids remove immune restraint.

Latent herpesvirus reservoirs

VZV, HSV, CMV and EBV persist in neural or haematopoietic compartments and reactivate according to the specific cellular or humoral defect.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Granuloma-dependent containment
TNF, interferon signalling and activated macrophages maintain organised tuberculosis control; blocking these pathways permits bacillary replication and extrapulmonary spread.
2
HBV immune escape
Loss of B- and T-cell pressure permits renewed transcription from persistent covalently closed circular DNA, followed by immune-mediated hepatitis as control returns.
3
Helminth hyperinfection
Corticosteroid exposure accelerates the Strongyloides autoinfective cycle, generating massive larval migration, mucosal injury and translocation of enteric bacteria.
4
Impaired test responsiveness
Lymphopenia, corticosteroids and severe illness reduce interferon and skin-test responses, creating indeterminate or false-negative results precisely when reactivation risk is high.
5
Loss of vaccine control
B-cell depletion and intensive transplantation weaken existing antibody and prevent new responses, allowing vaccine-preventable disease despite a remote immunisation history.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Possible active tuberculosisRed flag

Constitutional, respiratory, nodal, spinal, abdominal or neurological symptoms and abnormal imaging require site-specific microbiology before the result is classified as latent infection.

Previous hepatitis B

An HBsAg-negative, anti-HBc-positive pattern records prior natural infection and still carries reactivation risk during B-cell depletion or other intensive therapy.

Strongyloides exposure phenotype

Birth, residence or prolonged travel in tropical or subtropical settings, barefoot soil exposure, intermittent rash or gastrointestinal symptoms raises risk even without eosinophilia.

Absent varicella immunity

No dependable chickenpox or vaccination history should prompt VZV IgG testing early enough to offer a live vaccine before significant immunosuppression when appropriate.

Pre-existing immune suppression

Current corticosteroids, chemotherapy, advanced illness or lymphopenia increases false-negative cellular tests and may require combined testing, imaging or specialist interpretation.

Red flags requiring action

Cough, fever, weight loss, night sweats, haemoptysis, lymphadenopathy or abnormal chest imaging requires active-tuberculosis investigation and appropriate respiratory isolation before latent treatment.
Jaundice, coagulopathy, encephalopathy or major aminotransferase elevation with positive hepatitis markers needs urgent hepatology assessment rather than routine pre-treatment clearance.
Abdominal or respiratory deterioration, Gram-negative bacteraemia, meningitis or serpiginous rash after corticosteroids in an exposed person suggests Strongyloides hyperinfection.
A widespread vesicular rash, ocular symptoms, meningism or neurological change indicates active VZV or HSV disease, not merely absent immunity.
A negative IGRA, absent eosinophilia or negative antibody result during existing immunosuppression can be falsely reassuring and must not override a high-risk history or syndrome.
Rituximab, stem-cell transplantation, intensive chemotherapy and high-dose corticosteroids can create reactivation risk that requires specialist prophylaxis before every pending result is available.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

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
Structured exposure and treatment historyFirst step
Why
Set pre-test probability, identify active symptoms and determine which latent or vaccine-preventable infections matter for the planned mechanism.
Interpretation and limitations
Document countries and dates, TB contact and previous treatment records, viral-hepatitis and HIV risks, soil exposure, VZV history, vaccines, prior immunosuppression and urgency of the proposed therapy.
02
First-line TB screenFirst line
Why
Identify immune sensitisation and radiographic evidence of previous or current tuberculosis before biologic or substantial immunosuppressive treatment.
Interpretation and limitations
Use symptom assessment, chest radiography and an IGRA, with TST alone or alongside it when guideline and specialist context supports. Immunosuppression reduces sensitivity, and either positive test warrants active-disease exclusion.
03
Active-TB microbiology
Why
Confirm disease, determine infectivity and obtain susceptibility before preventive monotherapy creates resistance.
Interpretation and limitations
Collect sputum or involved-site material for rapid molecular assay, microscopy and culture when symptoms or imaging are compatible. A negative IGRA cannot replace these tests.
04
Complete hepatitis B serology
Why
Separate current infection, previous natural infection, vaccine immunity and susceptibility before a reactivation-prone regimen.
Interpretation and limitations
Request HBsAg, total anti-HBc and anti-HBs together. If HBsAg or anti-HBc is positive, add quantitative HBV DNA, ALT and specialist assessment; anti-HBs alone does not exclude occult past infection.
05
HCV and HIV testing
Why
Detect treatable chronic viral infection that changes immune-therapy safety, interactions, monitoring and transmission advice.
Interpretation and limitations
Confirm reactive HCV antibody with HCV RNA to identify current infection. Use a laboratory HIV antigen-antibody test and obtain HIV RNA when acute infection is possible despite initial serology.
06
Strongyloides assessment
Why
Prevent corticosteroid-triggered hyperinfection in people with relevant tropical or subtropical residence, travel or soil exposure.
Interpretation and limitations
Use serology before immune suppression when available and add serial or specialised stool examination if clinically indicated. Sensitivity falls during immune suppression; urgent high-risk treatment may justify expert-led presumptive therapy.
07
Vaccine and protocol-specific serology
Why
Identify preventable VZV and hepatitis B risk and meet transplant or drug-specific CMV, EBV and toxoplasma requirements.
Interpretation and limitations
Test VZV IgG when history is uncertain and use additional serology only when it changes prophylaxis or donor-recipient planning. Administer indicated live vaccines before, not during, major immunosuppression.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Active infection

Symptoms, organ abnormalities or positive pathogen detection may represent current disease requiring multidrug treatment rather than preventive monotherapy or observation.

False-positive immune assay

Low pre-test probability, technical variation and borderline IGRA results can generate apparent infection; repeat or alternative testing requires specialist contextual interpretation.

False-negative screening

Existing immunosuppression, lymphopenia, early infection and sampling error can conceal TB, Strongyloides or viral markers and should not overrule a compelling exposure history.

Vaccine-derived antibody

Isolated anti-HBs with negative anti-HBc reflects hepatitis B vaccination rather than previous natural infection and carries a different reactivation implication.

Resolved treated infection

Documented adequate tuberculosis or hepatitis treatment may reduce risk substantially, but incomplete records, reinfection and planned immune intensity determine whether reassessment is needed.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01BASELINEBuild the screening setFirst stepA biologic, targeted drug, conventional immunosuppressant, prolonged corticosteroid course, chemotherapy or transplantation is being planned.

1Define the treatment mechanism, expected intensity and start date, then take a structured infection, travel, vaccination and previous-treatment history.
2Check FBC, renal and liver profiles and complete core infection testing early enough to act on results without unnecessary therapeutic delay.
3Add exposure- and protocol-specific tests such as Strongyloides, VZV, CMV, EBV or toxoplasma rather than ordering an undirected universal panel.
4Assign each positive, indeterminate or pending result to a named TB, hepatology, infection, sexual-health, virology or tropical-medicine pathway.

02TB POSITIVEExclude disease before preventionIGRA, TST, history or chest imaging suggests tuberculosis infection or previous inadequately documented treatment.

1Reassess symptoms and imaging and obtain molecular and culture specimens from any plausible active site; use respiratory isolation when pulmonary disease is possible.
2Refer to a TB specialist, verify previous drug exposure and susceptibility risk, and do not give a latent regimen until active disease is reasonably excluded.
3Select three months of rifampicin plus isoniazid or six months of isoniazid from age, liver risk, pregnancy, interactions and planned immune therapy.
4For biologic therapy, agree the minimum completed preventive interval and monitoring with TB and prescribing specialists; BSR supports starting after at least one month in selected treated latent infection.

03HBV MARKERSStratify reactivation riskHBsAg or total anti-HBc is positive before an immune-modifying regimen.

1Obtain quantitative HBV DNA, ALT and liver assessment, confirm the exact planned medicine and classify HBsAg-positive versus HBsAg-negative, anti-HBc-positive status.
2Use hepatology to select antiviral prophylaxis for high-risk treatment such as B-cell depletion or active HBsAg-positive infection, including renal and pregnancy considerations.
3When monitoring without prophylaxis is appropriate, define the ALT and HBV DNA interval, action threshold and rapid access route before immunosuppression begins.
4Continue prophylaxis and surveillance for the specialist-defined period after the last immune-treatment dose because reactivation can be delayed.

04STRONGYLOIDES RISKPrevent steroid-triggered hyperinfectionRelevant endemic exposure is identified before corticosteroid or substantial cellular immune suppression.

1Send Strongyloides serology while reviewing eosinophil history, gastrointestinal or skin symptoms, prior ivermectin and possible Loa loa exposure.
2Treat confirmed chronic infection before non-urgent immune suppression and document response using the tropical-medicine follow-up plan.
3If high-dose corticosteroid cannot wait and exposure risk is material, obtain urgent tropical advice about presumptive ivermectin rather than relying on a pending or falsely negative test.
4For possible hyperinfection, admit, send stool and respiratory samples, culture blood for enteric bacteria and use daily expert-directed therapy until parasitological clearance criteria are met.

05VACCINATE AND PROCEEDClose preventable gapsScreening finds susceptibility or an incomplete vaccine schedule without active infection.

1Give indicated inactivated vaccines as early as possible, accepting that responses may be weaker once immune treatment starts but safety is generally preserved.
2Administer a required live vaccine only when the person is not significantly immunosuppressed and the Green Book interval before treatment can be completed.
3For HBsAg-negative, anti-HBc-negative, anti-HBs-negative patients, offer hepatitis B vaccination when risk or treatment pathway indicates and plan post-vaccine testing where required.
4Document the negative and positive results, prophylaxis, vaccine dates, residual uncertainty and circumstances that should trigger repeat testing after new exposure or travel.

Key medicines and prescribing safety4 treatments · regimens, roles and cautions

NICE-supported shorter preventive regimen after active tuberculosis has been excluded, particularly when interaction burden and hepatic assessment permit.

Rifampicin plus isoniazid for latent TB

Give daily for 3 months with pyridoxine under the TB service; a person at least 50 kg commonly receives rifampicin 600 mg plus isoniazid 300 mg once daily.

Rifampicin is a potent enzyme and transporter inducer affecting contraception, anticoagulants, corticosteroids, calcineurin inhibitors, azoles and antivirals; both agents can cause hepatitis, hypersensitivity and major toxicity.

NICE-supported alternative when rifamycin interactions are a major concern, including selected transplant or HIV-associated treatment plans.

Isoniazid for latent TB

Give isoniazid 300 mg orally once daily with pyridoxine for 6 months in a typical adult, supervised and modified by the TB service for weight, age, liver risk and pregnancy.

Obtain baseline liver assessment and monitor symptoms and tests by risk; neuropathy, hepatitis, seizures and interactions require prompt review, and preventive monotherapy must never treat unexcluded active disease.

Prevents reactivation during high-risk immunosuppression in HBsAg-positive and selected HBsAg-negative, anti-HBc-positive patients.

HBV nucleos(t)ide analogue prophylaxis

Use the hepatology regimen for entecavir or tenofovir, with exact dose and duration determined by HBV DNA, previous antiviral resistance, renal and bone health, pregnancy and immune-treatment risk.

Start before or with immunosuppression when indicated, check interactions and renal function, and never stop without a post-treatment HBV DNA and ALT surveillance plan.

Eradicates chronic Strongyloides before corticosteroid or major immunosuppression and can be used presumptively when urgent treatment and exposure risk justify it.

Ivermectin for chronic strongyloidiasis

Give 200 micrograms/kg orally once daily for 1 to 2 days for uncomplicated chronic infection under tropical-medicine advice; suspected hyperinfection requires a different daily-until-clearance specialist regimen.

Assess pregnancy, weight, possible Loa loa co-infection and neurological risk; immunosuppressed patients need expert follow-up because serology and stool tests can be falsely negative.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Disseminated tuberculosis

Loss of cellular containment can produce miliary, nodal, meningeal, spinal, abdominal or multisystem disease with reduced diagnostic test sensitivity and high mortality.

Fulminant hepatitis B

Reactivation can cause abrupt viral expansion, immune-mediated hepatocyte destruction, liver failure and interruption of essential chemotherapy or immune treatment.

Strongyloides hyperinfection

Accelerated larval migration causes enterocolitis, diffuse lung disease, Gram-negative sepsis or meningitis and disseminated infection with very high fatality.

Disseminated herpesvirus disease

Absent immunity or reactivation during cellular suppression can cause widespread skin, eye, lung, liver or CNS disease rather than a limited dermatomal illness.

Preventive-treatment harm

Hepatotoxicity, neuropathy, drug interactions, unnecessary delay and false reassurance can result when screening is interpreted without exposure probability and treatment urgency.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Maintain a result tracker that records the assay, date, immune state at sampling, interpretation, action, treatment owner and planned immunosuppression start date.
During latent-TB treatment, review adherence, hepatitis and neuropathy symptoms and obtain liver tests at baseline and thereafter according to age, abnormality and clinical risk.
For previous or current HBV, follow ALT and quantitative HBV DNA at the hepatology-defined interval during immunosuppression and for the required post-treatment period.
Repeat TB, viral or parasite risk assessment after a new exposure, prolonged travel, unexplained symptoms or a major escalation in immune therapy; a historic negative result is not lifetime clearance.
Check vaccine completion and response where guidance requires, while recording which live products are contraindicated by current treatment and when they may become safe.
Before starting immune therapy, confirm that active infection has been excluded where necessary, preventive medicine is tolerated and the patient knows which symptoms require urgent review.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

There is no latent-TB gold standard

IGRA and TST measure immune sensitisation rather than viable bacilli; exposure, imaging, immune state and previous treatment determine the final probability.

Anti-HBc changes the plan

Past natural HBV infection remains biologically relevant even with negative HBsAg and positive anti-HBs because intrahepatic viral templates can persist.

Eosinophils can disappear

Corticosteroids and Strongyloides hyperinfection may remove the eosinophilia that would otherwise prompt investigation, making geographic history more dependable than one count.

Urgency changes sequencing

Non-urgent biologic treatment can wait for infection prevention, whereas organ-threatening vasculitis or cancer may require simultaneous immune therapy and pathogen prophylaxis under specialist control.

Vaccines need lead time

Live vaccines require a safe interval before significant immune suppression, and even inactivated responses may improve when delivered before B-cell depletion or intensive treatment.

11Common pitfallsFrequent interpretation and management errors.

01
Calling a positive IGRA latent tuberculosis without asking about symptoms, reviewing chest imaging or sampling a possible active site.
02
Using HBsAg alone and missing anti-HBc-positive previous infection before rituximab or another high-risk regimen.
03
Treating anti-HBs positivity as proof that hepatitis B exposure was vaccination when total anti-HBc has not been measured.
04
Relying on absent eosinophilia or one negative stool microscopy result to exclude Strongyloides before high-dose corticosteroids.
05
Ordering broad serology without linking each result to prophylaxis, vaccination, treatment delay or a responsible specialist.
06
Assuming a negative baseline screen remains valid after new travel, household exposure or a later escalation from single-agent to combination immunosuppression.