Chronic Infections and Immune Burden

Infections are usually thought of as acute events: a fever, a cough, a course of antibiotics, recovery. But some infections persist for years or a lifetime, quietly affecting other systems, and some leave lasting consequences after the organism has gone. Recognising these chronic infections, and their effects on the immune system and beyond, is an important part of comprehensive assessment. So is recognising where the idea of hidden infection has been stretched beyond the evidence.

Chronic infections with established systemic effects

How chronic infections affect the body

• Direct tissue damage, as in hepatitis and Helicobacter pylori gastritis.
• Chronic inflammation, contributing to cardiovascular and metabolic risk.
• Cancer, through chronic inflammation and, for some viruses, direct effects on cell growth.
• Immune activation and ageing, as with cytomegalovirus.
• Autoimmunity, through molecular mimicry and other mechanisms.
• Nutritional effects, such as iron deficiency with Helicobacter pylori.

Screening based on risk

Most chronic infections are best identified through targeted screening based on risk factors rather than broad testing.

• Country of birth and travel: hepatitis B, tuberculosis, Strongyloides and other infections endemic in particular regions.
• Sexual history and injecting drug use: HIV, hepatitis B and C, syphilis.
• Past medical history: blood transfusions before screening was introduced, previous imprisonment, dialysis.
• Planned immunosuppression: screening for hepatitis B, latent tuberculosis and, where relevant, Strongyloides before starting biologics, chemotherapy or high dose steroids.
• Symptoms and findings: iron deficiency, dyspepsia, abnormal liver tests.
• Population programmes: some countries recommend one off testing for hepatitis C or HIV in all adults.

Asking about vaccination status is equally important: hepatitis B, HPV and other vaccines prevent chronic infection.

Post infection syndromes

Some people develop persistent symptoms after an infection has resolved.

Long COVID, or post COVID condition, describes symptoms persisting for months after infection, including fatigue, breathlessness, cognitive difficulties and post exertional symptom exacerbation. It is a real and common condition, with mechanisms under active investigation, including persistent immune activation, viral persistence, autonomic dysfunction and vascular changes.

Myalgic encephalomyelitis or chronic fatigue syndrome often follows an infection. Its hallmark is post exertional malaise. Management focuses on symptom relief, pacing and support.

Post infection irritable bowel syndrome follows gastroenteritis in a proportion of people.

Post treatment Lyme disease syndrome describes persistent symptoms after appropriately treated Lyme disease.

These conditions deserve recognition and support. Their existence is well established even where mechanisms and treatments are still being studied.

Where the concept is stretched

A different phenomenon is the attribution of wide ranging, unexplained symptoms to hidden chronic infections that conventional tests supposedly miss. The best known example is chronic Lyme disease as used in some practices, diagnosed on the basis of symptoms and tests from laboratories using unvalidated methods or interpretation criteria, and treated with prolonged courses of antibiotics.

The evidence does not support this approach. Randomised trials of prolonged antibiotic treatment in people with persistent symptoms attributed to Lyme disease, including a large European trial, found no benefit over shorter treatment or placebo, while prolonged intravenous antibiotics have caused serious harms, including catheter infections and deaths. Similar concerns apply to claims about hidden mould, parasite or viral infections diagnosed by unvalidated tests.

Patients who receive these diagnoses have real symptoms and often feel dismissed by conventional care. The appropriate response is to take their symptoms seriously, look carefully for identifiable causes, including genuine infections tested for with validated methods, and address their symptoms and function, rather than to endorse unvalidated diagnoses or prolonged antimicrobial treatment.

A functional approach

1. Take an exposure history: birthplace, travel, occupation, sexual history, animal exposures, tick bites, transfusions.
2. Screen based on risk using validated tests.
3. Treat established infections through appropriate medical care.
4. Support vaccination as prevention.
5. Recognise post infection syndromes and support patients with them, respecting pacing where post exertional symptoms are present.
6. Avoid unvalidated diagnoses and prolonged empirical antimicrobials.
7. Address immune resilience: nutrition, sleep, stress, metabolic health, oral health.

An illustrative case

A 52 year old man born in West Africa, living in Europe for 20 years, has fatigue, mildly raised liver enzymes and iron deficiency. He has been told he may have a chronic parasitic or mould infection and has been offered an expensive detox protocol. His practitioner takes an exposure history and discusses it with his doctor, who tests for hepatitis B and C, Helicobacter pylori and Strongyloides. He has chronic hepatitis B, previously undiagnosed, and Helicobacter pylori infection. He is referred to a liver specialist, starts antiviral monitoring and treatment as advised, and receives eradication therapy for Helicobacter pylori. His iron deficiency is treated. His family members are offered hepatitis B testing and vaccination. The genuine infections were identified with validated tests, and they were treatable.

Real infections, real evidence

Chronic infections are an important and sometimes overlooked contributor to chronic disease, and many can be prevented, cured or controlled. Finding them requires a careful exposure history and validated testing, not assumptions about hidden infections that tests cannot confirm.