2.7 Host Risk Factors & Emerging Infectious Disease Threats
Key Takeaways
- Intrinsic risk factors such as age extremes, immunosuppression, diabetes, and malnutrition cannot be modified, while extrinsic factors such as devices, surgery, and antimicrobial exposure are the targets of infection prevention.
- Invasive devices are the single largest modifiable driver of healthcare-associated infection, which is why device utilization ratios and daily necessity reviews sit at the center of prevention bundles.
- Travel history, vaccination status, and epidemiologic exposure are essential triage elements for identifying imported measles, viral hemorrhagic fevers, avian influenza, and drug-resistant tuberculosis.
- CDC's Health Alert Network, WHO Disease Outbreak News, and state and local health department advisories are the standard channels for staying informed about current and emerging threats.
- Candida auris, carbapenem-resistant organisms, measles resurgence, mpox, and highly pathogenic avian influenza are the emerging threats most likely to appear in current exam scenarios.
2.7 Host Risk Factors & Emerging Infectious Disease Threats
Quick Answer: Intrinsic risk factors belong to the patient and cannot be changed (age, immunosuppression, diabetes, malnutrition). Extrinsic risk factors come from care delivery and can be changed (devices, surgery, antimicrobials, length of stay). Infection prevention lives almost entirely in the extrinsic column. Horizon-scanning for emerging threats runs through CDC HAN, WHO Disease Outbreak News, and state/local health department advisories.
Intrinsic Risk Factors
| Factor | Mechanism |
|---|---|
| Age extremes | Neonates have immature immunity; older adults have immunosenescence, thinner skin, and blunted fever response |
| Neutropenia | Absolute neutrophil count <500 cells/µL confers profound risk; <100 is critical. Drives protective environment housing for transplant patients |
| Immunosuppressive therapy | Corticosteroids, biologics, calcineurin inhibitors, chemotherapy |
| Transplantation | Solid organ and hematopoietic cell recipients — risk profile shifts by time since transplant |
| Advanced HIV | CD4-dependent opportunistic infection risk |
| Diabetes mellitus | Impaired neutrophil function, microvascular disease, poor wound healing; hyperglycemia is an independent SSI risk factor |
| Malnutrition / hypoalbuminemia | Impaired wound healing and antibody production |
| Obesity | Reduced tissue antibiotic penetration, larger wound surface, higher SSI risk |
| Burns and major skin loss | Destruction of the primary mechanical barrier |
| Chronic organ disease | COPD, cirrhosis, end-stage renal disease, heart failure |
Extrinsic Risk Factors — Where Prevention Works
| Factor | Prevention lever |
|---|---|
| Central venous catheters | Insertion bundle, chlorhexidine skin prep, daily necessity review, prompt removal |
| Urinary catheters | Avoid placement, use alternatives, nurse-driven removal protocols |
| Mechanical ventilation | Sedation interruption, spontaneous breathing trials, head-of-bed elevation, oral care |
| Surgery | Prophylaxis timing, normothermia, glycemic control, appropriate hair removal (clippers, never razors) |
| Antimicrobial exposure | Stewardship — antibiotics are the dominant risk factor for C. difficile infection and MDRO acquisition |
| Length of stay / ICU days | Every additional day is additional exposure |
| Total parenteral nutrition | Line dependence plus a growth-supporting infusate |
| Prior colonization | MRSA, VRE, CRE, C. auris carriage predicts later infection |
Exam Tip: When a stem asks for the most effective way to reduce a device-associated infection, the answer is almost always removing or avoiding the device, not adding a product. The device utilization ratio exists precisely to measure this exposure.
Exposure History: Travel, Vaccination, and Contact
Three questions at triage change management immediately:
- Where have you been in the last 21–30 days?
- What are you vaccinated against?
- Who or what have you been exposed to?
| Travel / exposure clue | Consider | Immediate IPC action |
|---|---|---|
| Febrile traveler from a malaria-endemic region | Malaria, typhoid, dengue | Standard Precautions; urgent thick/thin smears — malaria is not transmitted person-to-person |
| Fever + rash + coryza, unvaccinated | Measles | Airborne Precautions immediately; mask the patient, AIIR, exclude susceptible staff |
| Fever within 21 days of travel to a viral hemorrhagic fever area | Ebola, Marburg, Lassa | Identify–Isolate–Inform; notify public health immediately |
| Poultry, dairy cattle, or wild bird contact with respiratory illness or conjunctivitis | Highly pathogenic avian influenza (H5N1) | Airborne + contact + eye protection; notify public health |
| Cough >3 weeks, weight loss, night sweats, high-incidence country of origin | Tuberculosis | Airborne Precautions, AIIR, three sputum specimens |
| Healthcare exposure abroad or transfer from an international facility | CRE, C. auris, MDR organisms | Pre-emptive contact precautions and admission screening |
Vaccination status is itself a risk factor. Falling measles coverage has restored a pathogen with a reproduction number of 12–18 and airborne persistence for up to two hours after the patient leaves the room — the single most transmissible agent an IP is likely to encounter.
Staying Informed: The Horizon-Scanning Task
The blueprint requires candidates to stay informed about current and emerging local and global health threats. That is an operational habit with defined sources:
| Source | What it delivers |
|---|---|
| CDC Health Alert Network (HAN) | Official U.S. advisories, alerts, and updates — subscribe directly |
| WHO Disease Outbreak News | Verified international outbreak reports |
| State and local health departments | Jurisdiction-specific alerts, reporting mandates, and situational awareness; usually the first notice an IP receives about local activity |
| CDC Emerging Infectious Diseases and MMWR | Peer-reviewed and surveillance reporting |
| ProMED-mail | Early, informal global event reporting |
| ECDC / PHAC | European and Canadian equivalents for international facilities |
| Professional societies (APIC, SHEA, IDSA) | Practice-oriented interpretation and guidance |
Current threats worth knowing by name
- Candida auris — multidrug-resistant yeast, persistent skin colonization, environmental survival, frequent misidentification on older laboratory platforms, requires sporicidal or C. auris-specific EPA List P disinfectants
- Carbapenem-resistant Enterobacterales and carbapenemase-producing organisms — plasmid-mediated resistance that spreads between species
- Measles — resurgent with declining vaccination coverage
- Mpox — clade-dependent transmission and precaution decisions
- Highly pathogenic avian influenza A(H5N1) — expanding mammalian and dairy-herd involvement with occupational exposures
- Drug-resistant tuberculosis — MDR and XDR strains requiring prolonged airborne isolation
- Emerging respiratory viruses — the pandemic-preparedness planning assumption
This is a One Health problem: human, animal, and environmental health are a single system, which is why avian influenza in dairy cattle becomes a hospital occupational health question.
Which risk factor for healthcare-associated infection is extrinsic and therefore a direct target for infection prevention intervention?
An unvaccinated patient presents to the emergency department with fever, cough, coryza, conjunctivitis, and a maculopapular rash after international travel. What is the immediate infection prevention action?
Which source provides official United States public health advisories and alerts that an infection preventionist should subscribe to for awareness of emerging threats?
A patient is transferred from an international hospital where they were treated for several weeks. Which pre-emptive infection prevention measure is most appropriate on admission?