Reservoir (Chain of Infection)
Key Points
- The reservoir is the habitat or source in which a pathogen survives, grows, and multiplies — the “home” of the infectious agent; second link in the chain-of-infection
- Most pathogens prefer warm, moist, dark environments — making the human body the most common reservoir
- A carrier harbors a pathogen without displaying symptoms — unknowingly spreading infection
- Nursing goal: eliminate or contain the reservoir to break the chain of infection before transmission occurs
- Healthcare equipment (medication carts, glucose monitors, infusion pumps) can serve as environmental reservoirs
- Reservoirs include humans, animals/insects, food, water, and contaminated surfaces or devices.
Definition
The reservoir is the habitat in which a pathogen survives, grows, and multiplies between transmissions to a new host. Every pathogen requires a reservoir to persist; without a suitable environment, it cannot cause disease. The reservoir is the second link in the chain-of-infection (following the causative agent) and precedes the portal-of-exit through which the pathogen leaves.
Types of Reservoirs
Human Reservoirs
The human body is the most common reservoir for infectious pathogens because it provides the warm, moist, and nutrient-rich environment that supports pathogen survival.
| Human Reservoir Type | Description | Example |
|---|---|---|
| Actively infected person | Shows signs and symptoms of infection; knows they are ill | Patient with active tuberculosis, COVID-19, influenza |
| Asymptomatic carrier | Harbors and transmits the pathogen without showing illness; may be unaware of their carrier status | Healthy hepatitis B carrier; MRSA colonization |
| Incubation period carrier | Infected but not yet symptomatic; transmissible before illness appears | Pre-symptomatic COVID-19 spreader |
| Convalescent carrier | Recovered from illness but still shedding pathogen | Post-illness typhoid carrier |
Animal Reservoirs (Zoonotic Sources)
Pathogens with animal reservoirs can be transmitted to humans as “accidental hosts.” Transmission from animal reservoirs to humans is called zoonosis.
| Animal Reservoir | Disease | Pathogen |
|---|---|---|
| Rodents | Plague, Leptospirosis | Yersinia pestis, Leptospira |
| Sheep, cattle | Anthrax | Bacillus anthracis |
| Mosquitoes | West Nile virus, ZIKA | Flaviviridae, Zika virus |
| Bats | Rabies | Rabies virus |
| Birds | Avian influenza | Influenza A H5N1 |
Environmental Reservoirs
Soil, water, and inanimate surfaces can serve as reservoirs for pathogens capable of surviving outside a living host.
- Soil: Clostridium tetani (tetanus) and Clostridium botulinum (botulism) survive in soil for years and remain infectious
- Water: Vibrio cholerae (cholera), Legionella (Legionnaire’s disease) survive in water sources
- Food: Improperly handled or contaminated food can carry enteric pathogens and sustain transmission cycles
- Healthcare surfaces: Medication carts, vital signs equipment, bed rails, call lights, IV pumps, glucometers — must be cleaned between patients
- Medical devices: Indwelling urinary catheters, IV catheters, ventilators — provide reservoirs and portals of entry simultaneously
Clinical Significance
Normal Flora as Reservoir
Normal body flora — beneficial organisms that live on/in the body without causing harm — can become pathogenic when displaced to a different body site:
- Escherichia coli (harmless in the gut) → causes UTI if introduced into the urinary tract
- Staphylococcus aureus (normal skin colonizer) → causes wound infection if it enters a surgical incision
- Candida albicans (normal oral flora) → causes oral candidiasis in immunocompromised patients or after broad-spectrum antibiotic exposure
Healthcare-Associated Reservoirs
Hospitalized patients are surrounded by reservoirs unique to the healthcare environment:
- Colonized patients and healthcare workers (MRSA, VRE)
- Contaminated equipment shared between patients
- High-touch surfaces (bed rails, call buttons, computer keyboards, doorknobs)
Nursing Interventions to Eliminate Reservoirs
| Strategy | Action |
|---|---|
| Wound care | Debride devitalized tissue; change dressings using aseptic technique |
| Equipment cleaning | Disinfect all shared patient equipment between uses |
| Patient hygiene | Daily bathing, oral care, perineal care to reduce microbial load |
| Environmental cleaning | High-touch surface disinfection at shift change and discharge |
| Isolation | Cohort patients with same organism; contain reservoir in the room |
| Screening | MRSA/VRE swabs on admission to identify asymptomatic carriers |
| Colonization management | Decolonization protocols (chlorhexidine bathing, nasal mupirocin) for MRSA carriers |
Related Concepts
- chain-of-infection — Complete model of infection transmission; reservoir is the second link
- portal-of-exit — The pathway by which the pathogen leaves the reservoir
- mode-of-transmission — How pathogen travels from reservoir to susceptible host
- susceptible-host — Final link; the person at risk of infection from the reservoir
- healthcare-associated-infections — HAIs often arise from hospital-specific reservoirs
- standard-precautions — Universal measures applied to all patients regardless of reservoir awareness