ID: Hospital infection, the immunocompromised host, vaccination and public health

• Hospital infection: Healthcare-Associated Infection | Clostridioides difficile Infection | MRSA | Resistant Gram-Negatives — ESBL and CPE | Hospital-Acquired Pneumonia | Catheter-Associated Urinary Infection | Line Infections | Norovirus and Ward Outbreaks
• The immunocompromised host: Neutropenic Sepsis | Infections After Transplantation | Biologics, Steroids and Other Immunosuppressants | Primary Immunodeficiency
• Vaccination: How Vaccines Work and Who Shouldn't Have Them | The UK Vaccination Programme | Vaccines for Special Groups
• Public health: Contacts and Prophylaxis | Managing Outbreaks
• Revision: Prevention at a Glance | Spot the Diagnosis | Exam-style Scenarios | Key Points | Guidelines and Further Reading

🏥 Hospital infection, the immunocompromised host, vaccination and public health — page 6 (the last page) of the Infectious Diseases chapter. Many infections are caused by healthcare — catheters, lines, antibiotics, surgery and shared wards — and many are preventable. A growing number of patients are immunosuppressed by cancer treatment, transplant drugs, steroids and biologics, and they get different infections that progress faster. Vaccination and public health action protect everyone else.
Your four questions for every patient: Did the infection come from healthcare, and could it have been prevented (devices, antibiotics, hygiene)? Is the patient immunosuppressed — and in what way (neutrophils, antibodies, T cells, spleen, complement)? What screening, prophylaxis and vaccines do they need? Do contacts, staff or the ward need protecting?

Healthcare-Associated Infection

• Healthcare-associated infections (HCAIs) — affect a significant proportion of hospital inpatients at any time; they prolong stays, drive resistance and kill.
• The commonest — pneumonia (including aspiration), urinary infections (mostly catheter-related), surgical site infections, bloodstream infections (lines and cannulas), C. difficile, norovirus and other GI infections.
• Key causes — invasive devices, surgery, antibiotics (C. difficile and resistance), immunosuppression, frailty, and spread between patients on hands and equipment.
• Prevention (see Infection Prevention and Control on page 1):
  • Hand hygiene at the five moments; bare below the elbows.
  • Device stewardship — only insert lines and catheters when needed, use aseptic technique, review daily, remove as soon as possible.
  • Antimicrobial stewardship — Start Smart — Then Focus.
  • Screening and isolation (MRSA, CPE), environmental cleaning, care bundles (central lines, ventilators, surgical sites), staff vaccination.
• Mandatory surveillance in England — MRSA, MSSA, E. coli, Klebsiella and Pseudomonas bloodstream infections, C. difficile infection, and surgical site infections after some operations; serious cases get a post-infection review.

Clostridioides difficile Infection

• C. difficile — a spore-forming anaerobic bacterium; toxins (A and B) damage the colon. Spores survive on surfaces for months and are not killed by alcohol gel.
• Risk factors — antibiotics (especially clindamycin, cephalosporins, co-amoxiclav and quinolones; any antibiotic can cause it), age over 65, hospital or care home stay, PPIs, immunosuppression, IBD, recent bowel surgery, tube feeding.
• Features — diarrhoea (Bristol type 5–7), abdominal pain and cramps, fever, raised white count; severe disease can cause ileus without diarrhoea, toxic megacolon (distension, tenderness), perforation, AKI and death.
• Testing — only test unformed stool when there is no other clear cause (e.g. laxatives); two-step test:
  • GDH or PCR (shows the organism is present) then toxin test.
  • Toxin positive — C. difficile infection; GDH or PCR positive but toxin negative — possible carriage (isolate; treat only if clinically likely).
  • Don't repeat a positive test within 28 days or test for "clearance".
• Signs of severe infection — white count over 15 × 10⁹/L, creatinine rising over 50% above baseline, temperature over 38.5°C, signs of severe colitis (abdominal signs, distension, imaging); life-threatening — hypotension, ileus, toxic megacolon, perforation.
• Management (NICE NG199):
  • Isolate in a side room with its own toilet; gloves and aprons; soap and water hand washing; chlorine-based cleaning.
  • Stop the causing antibiotic if possible (or switch to a lower-risk one) and review PPIs and laxatives; avoid antimotility drugs.
  • Fluids and electrolytes; daily review of stool chart, abdomen, white count and creatinine.
  • First episode — oral vancomycin 125 mg four times daily for 10 days; fidaxomicin 200 mg twice daily for 10 days if vancomycin fails.
  • Life-threatening — oral vancomycin 500 mg four times daily (plus IV metronidazole), urgent surgical and specialist review (colectomy may be needed); vancomycin by NG tube or rectally in ileus.
  • Recurrence (about 1 in 5) — fidaxomicin; faecal microbiota transplant after two or more recurrences.
• Prevention — antibiotic stewardship (fewer broad-spectrum drugs, shorter courses), stop unnecessary PPIs, rapid isolation and testing, environmental cleaning.

MRSA

• Meticillin-resistant Staphylococcus aureus — resistant to flucloxacillin and most other beta-lactams; colonises the nose, skin, wounds and throat.
• Screening — targeted screening of higher-risk patients (e.g. before elective surgery, admissions to ICU, renal and other high-risk units, previous MRSA) according to local policy (nose, groin, wounds, catheter urine).
• Decolonisation — nasal mupirocin (or alternative) and chlorhexidine body wash for 5 days, especially before surgery; repeat screening.
• Infection control — contact precautions (side room where possible), hand hygiene, dedicated equipment.
• Treatment of MRSA infection — vancomycin or teicoplanin (serious infections), linezolid or daptomycin (alternatives), doxycycline or co-trimoxazole (milder skin and soft tissue infections, by sensitivity); rifampicin or fusidic acid only in combination.
• Community-associated MRSA (often PVL-producing S. aureus) — recurrent boils, abscesses and occasionally severe necrotising pneumonia in otherwise healthy young people; drain abscesses, decolonise the household.
• MRSA bacteraemia — managed as S. aureus bacteraemia (see page 2); a post-infection review looks for lessons (lines, screening, decolonisation).

Resistant Gram-Negatives — ESBL and CPE

• ESBL-producing Enterobacterales (E. coli, Klebsiella) — common, including in the community; carriage in the gut is often silent:
  • Infections — UTI, pyelonephritis, biliary and abdominal sepsis, pneumonia.
  • Treatment — serious infections usually need a carbapenem (meropenem or ertapenem); alternatives by sensitivity (piperacillin–tazobactam sometimes, temocillin, aminoglycosides); oral options for UTI — nitrofurantoin, fosfomycin, pivmecillinam.
  • Flag on records so future empirical antibiotics are chosen wisely.
• Carbapenemase-producing Enterobacterales (CPE) — resistant to carbapenems and often almost everything else:
  • Screen (rectal swab) patients who in the last 12 months were in hospital abroad, in UK hospitals with CPE problems, or were previously positive; isolate until results are known (local policy).
  • Strict contact precautions; inform IPC; treatment needs specialist advice (e.g. ceftazidime–avibactam, colistin, combination therapy).
• Other resistant organisms — Pseudomonas and Acinetobacter (ICU, burns, ventilators), VRE (haematology, renal, ICU), Candida auris.
• Colonisation is not infection — don't treat a positive screening swab; do use the information to choose antibiotics if the patient becomes septic.

Hospital-Acquired Pneumonia

• Hospital-acquired pneumonia (HAP) — pneumonia starting 48 hours or more after admission; ventilator-associated pneumonia (VAP) — after 48 hours of mechanical ventilation.
• Organisms — early (under about 5 days) often community organisms; later or after recent antibiotics — Gram-negatives (including Pseudomonas, Klebsiella, ESBL), S. aureus (including MRSA).
• Diagnosis — new chest X-ray changes plus fever, purulent sputum, rising oxygen needs or white count; send sputum (or ETT aspirate in VAP) and blood cultures; consider other causes (PE, heart failure, atelectasis, aspiration pneumonitis).
• Treatment (NICE NG139; local guidelines) — non-severe and lower risk of resistance: oral options (e.g. co-amoxiclav, doxycycline); severe or higher risk of resistance: IV broad-spectrum (e.g. piperacillin–tazobactam) ± MRSA cover; review at 48–72 hours; usually 5–7 days in total.
• Aspiration — chemical pneumonitis after aspiration often settles without antibiotics; aspiration pneumonia is treated like HAP (routine anaerobic cover isn't usually needed).
• Prevention — head of bed raised, oral care, swallow assessment after stroke, early mobilisation, avoiding unnecessary sedation, minimising ventilation (sedation holds, VAP bundles), pneumococcal and influenza vaccination.

Catheter-Associated Urinary Infection

• The biggest risk is having a catheter — risk rises each day; most catheter urine becomes colonised (bacteriuria) within weeks.
• Only use catheters when needed — urinary retention, accurate output monitoring in critical illness, some surgery, end-of-life comfort; not for convenience or incontinence alone; daily review and early removal (nurse-led removal protocols).
• Don't dipstick catheter urine and don't treat asymptomatic bacteriuria — treat only symptoms (fever, rigors, loin pain, new confusion with no other cause, suprapubic pain, haematuria).
• Management (NICE NG113):
  • Consider removing the catheter, or change it if it has been in for more than 7 days, before starting antibiotics — and send a urine sample from the new catheter.
  • Antibiotics per local guidance and previous cultures (e.g. nitrofurantoin or trimethoprim for lower symptoms if suitable; IV options if systemically unwell); usually 7 days.
• Prevention — aseptic insertion, closed drainage, bag below the bladder, regular emptying with clean technique, catheter passport, trial without catheter.

Line Infections

• Peripheral cannulas — phlebitis and S. aureus bacteraemia; check every shift (VIP score); remove at the first sign of phlebitis and when no longer needed; avoid "just in case" cannulas.
• Central venous catheters, PICCs, ports and dialysis lines — central line-associated bloodstream infection (CLABSI):
  • Features — fever, rigors (especially during or after flushing the line), redness or pus at the exit site or along the tunnel, sepsis without another source.
  • Paired blood cultures (line and peripheral) — line cultures that become positive more than 2 hours before peripheral ones suggest the line is the source.
  • Organisms — coagulase-negative staphylococci, S. aureus, Gram-negatives (including Pseudomonas), enterococci, Candida.
• Remove the line if there is S. aureus, Pseudomonas, Candida or mycobacteria, tunnel or pocket infection, severe sepsis, persistent bacteraemia after 72 hours, endocarditis or septic thrombosis; line salvage (antibiotics plus antibiotic "lock" solution) may be tried for some CoNS infections in patients with few alternatives (e.g. long-term parenteral nutrition).
• Prevention — insertion bundles (hand hygiene, full barrier precautions, 2% chlorhexidine skin preparation, best site), aseptic non-touch technique for every access, chlorhexidine dressings, daily review of need.

Norovirus and Ward Outbreaks

• Norovirus ("winter vomiting bug") — the commonest cause of ward closures; incubation 12–48 hours; sudden vomiting (often projectile) and diarrhoea for 1–3 days; very infectious (aerosols from vomiting, contaminated surfaces); immunity is short-lived.
• Vulnerable patients — older and frail people (dehydration, AKI, falls), the immunosuppressed (prolonged infection).
• Control:
  • Isolate or cohort affected patients; close bays to admissions; inform the IPC team.
  • Soap and water for hands (alcohol gel is less effective); gloves, aprons and fluid-resistant masks when cleaning up vomit.
  • Enhanced cleaning with chlorine-based products; restrict visitors and staff movement between areas.
  • Staff stay off work until 48 hours symptom-free.
  • Send stool samples (PCR) from early cases to confirm.
• Other ward outbreaks — C. difficile, influenza, COVID-19, CPE, VRE, scabies, invasive group A strep (maternity, burns); recognising clusters early is key.

Neutropenic Sepsis

• Definition — neutrophil count 0.5 × 10⁹/L or less with a temperature over 38°C or other signs or symptoms of sepsis (NICE CG151); most often 7–14 days after chemotherapy.
• Signs may be subtle — little pus or inflammation without neutrophils; steroids mask fever; some patients present feeling "unwell" or cold and shivery.
• Immediate management:
  • Treat as an emergency — IV piperacillin–tazobactam within 1 hour of arrival (local alternative if penicillin-allergic), without waiting for the blood count if chemotherapy was recent.
  • Blood cultures (peripheral and from each line lumen), FBC, U&E, LFTs, CRP, lactate, urine, chest X-ray if respiratory symptoms; examine mouth, skin, line sites, chest, perineum (no rectal examination).
  • Don't routinely add an aminoglycoside or glycopeptide; add vancomycin for suspected line infection, MRSA, severe sepsis or skin infection.
• After 48–72 hours — tailor to cultures; low-risk patients (e.g. by MASCC score) may switch to oral antibiotics or go home with close follow-up.
• Persistent fever for 4–7 days despite antibiotics — look for fungal infection (CT chest, galactomannan) and consider empirical antifungal therapy.
• Prevention — patient education (the chemotherapy alert card and 24-hour helpline), G-CSF and antibacterial or antifungal prophylaxis in high-risk regimens.

⚠️ Safety Pearl: A patient who has had chemotherapy and is unwell with a fever has neutropenic sepsis until proven otherwise. Antibiotics go in within 1 hour — before the blood count comes back.

Infections After Transplantation

• Prophylaxis — co-trimoxazole (PCP), valganciclovir or monitoring for CMV, antifungals in some, vaccines before transplant.
• Stem cell transplant — prolonged neutropenia (bacterial and fungal infections), then T-cell deficiency (CMV, adenovirus, PCP), graft-versus-host disease and its treatment (steroids) adding further risk; haemorrhagic cystitis (BK virus, adenovirus).
• Drug interactions — tacrolimus, ciclosporin, sirolimus and everolimus levels are raised by macrolides and azoles and lowered by rifampicin (see the Renal Anatomy, Physiology and Pharmacology chapter) — always check before prescribing.
• Fever in a transplant patient — may also be rejection, drug reaction or PTLD; involve the transplant team early; signs of infection may be muted.
• Live vaccines are contraindicated after transplant.

Biologics, Steroids and Other Immunosuppressants

• Screen before starting biologics and strong immunosuppression:
  • TB — history, chest X-ray, IGRA; treat latent TB first (usually at least 1 month before the biologic, per specialist advice).
  • Hepatitis B (HBsAg, anti-HBc), hepatitis C, HIV.
  • VZV immunity (vaccinate if non-immune and there is time).
  • Strongyloides serology in people from endemic areas.
• PCP prophylaxis (co-trimoxazole) — considered for people on high-dose steroids for long periods, especially combined with other immunosuppressants, and for many chemotherapy and transplant regimens.
• Vaccinate before immunosuppression where possible — pneumococcal, influenza, COVID-19, shingles (non-live), hepatitis B; give live vaccines (e.g. MMR, varicella) at least 4 weeks before starting; no live vaccines during treatment.
• Babies exposed to biologics in late pregnancy (e.g. infliximab) — avoid live vaccines (e.g. rotavirus, BCG) in the first months (specialist advice).

Primary Immunodeficiency

• Suspect immunodeficiency with infections that are SPUR — Serious, Persistent, Unusual (opportunistic organisms or sites) or Recurrent — or with failure to thrive, family history, or autoimmunity with infections. Secondary causes (drugs, HIV, CLL, myeloma, nephrotic syndrome, protein loss, malnutrition) are far more common — check them first.

• First tests — FBC and film, immunoglobulins (IgG, IgA, IgM), specific antibody responses to vaccines (tetanus, pneumococcal), lymphocyte subsets, complement (CH50, AH50), HIV test; refer to clinical immunology.
• Treatment — prophylactic antibiotics, immunoglobulin replacement (IV or subcutaneous) for antibody deficiency, avoid live vaccines in significant immunodeficiency, stem cell transplant or gene therapy for SCID and some others.
• Hereditary angioedema (C1 inhibitor deficiency) — recurrent swelling without urticaria, abdominal attacks; not an infection problem but a complement disorder (see the Urticaria and Blistering chapter).

How Vaccines Work and Who Shouldn't Have Them

• Vaccines train the immune system to recognise an organism or toxin so it can respond fast on exposure; herd immunity protects people who can't be vaccinated when enough others are.
• Types:
  • Live attenuated — MMR, varicella, rotavirus, nasal flu (children), BCG, yellow fever, oral typhoid — strong immunity but can cause disease in the immunosuppressed.
  • Inactivated, subunit, toxoid, conjugate — e.g. tetanus, diphtheria, pertussis, polio (injected), Hib, pneumococcal, meningococcal, hepatitis A and B, HPV, injectable flu, shingles (Shingrix), RSV.
  • mRNA and viral vector vaccines — COVID-19.
• Contraindications:
  • Anaphylaxis to a previous dose or a vaccine component (rare).
  • Live vaccines — significant immunosuppression (chemotherapy, transplant, high-dose steroids — e.g. prednisolone 20 mg or more daily for 2 weeks or longer, biologics, advanced HIV) and pregnancy.
• Not contraindications — mild illness without fever, egg allergy (MMR and most flu vaccines can be given — check the Green Book), prematurity (vaccinate by chronological age), breastfeeding, a family history of reactions, stable neurological conditions, being on antibiotics.
• Common side effects — sore arm, mild fever, irritability; MMR can cause a mild rash or fever 7–10 days later. Fainting after injection is common in teenagers.
• Vaccine hesitancy — listen, acknowledge concerns, give clear information (MMR is not linked to autism), and keep the conversation open.

The UK Vaccination Programme

• Catch-up — check vaccination history for migrants, people who missed doses, and adults (MMR at any age if unvaccinated).
• Pertussis vaccine in pregnancy protects babies in the first weeks of life, before their own vaccines work.

Vaccines for Special Groups

• No spleen or splenic dysfunction (including sickle cell disease) — pneumococcal, Hib/MenC, MenACWY, MenB, annual influenza, COVID-19; lifelong antibiotic advice and stand-by antibiotics (see the Haematology Anatomy, Physiology and Pharmacology chapter).
• Immunosuppression — inactivated vaccines (pneumococcal, influenza, COVID-19, Shingrix, hepatitis B as indicated); give before treatment starts where possible; avoid live vaccines; household contacts should be vaccinated (including against flu and varicella) to protect them.
• Chronic disease — heart, lung, kidney, liver disease and diabetes — influenza, pneumococcal, COVID-19; hepatitis A and B for chronic liver disease; hepatitis B for CKD and dialysis.
• Healthcare workers — hepatitis B (check antibody response), MMR (two doses or proof of immunity), varicella (if non-immune), annual influenza, COVID-19, BCG for some at-risk roles, pertussis for those working with newborns in some settings.
• Men who have sex with men — hepatitis A and B, HPV (up to age 45), mpox (if at higher risk), MenB in some outbreaks.
• People who inject drugs — hepatitis A and B, tetanus.
• Travellers — see the Tropical and Travel Medicine page.
• Contacts of TB — BCG for unvaccinated infants and children at higher risk (BCG is offered to babies in high-incidence areas or with a parent or grandparent from a high-incidence country).

Contacts and Prophylaxis

Managing Outbreaks

• An outbreak — two or more linked cases of the same infection, or more cases than expected in a place or time (e.g. on a ward, in a care home, school or restaurant).
• Steps:
  • Recognise it — clusters of diarrhoea, respiratory illness, resistant organisms or unusual infections.
  • Confirm the diagnosis — appropriate samples; agree a case definition.
  • Control spread — isolation or cohorting, closing bays or wards to admissions, enhanced cleaning, hand hygiene, PPE, staff exclusion, visitor restrictions.
  • Inform — the infection prevention and control team, microbiology, and UKHSA (and notify where required).
  • Find the source — food, water, equipment, a colonised person, a contaminated environment (whole genome sequencing helps link cases).
  • Communicate with staff, patients and families; record actions; declare the outbreak over (usually after two incubation periods without new cases); learn lessons.
• Community outbreaks — schools and nurseries (exclusion advice), care homes (vaccination, antiviral prophylaxis for influenza), food premises (environmental health), prisons and hostels (TB, hepatitis).
• The doctor's duties — notify suspected notifiable diseases, report clusters, follow advice, and protect colleagues (vaccination, staying off work when infectious).

Prevention at a Glance

Spot the Diagnosis