Chain of Infection

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Chain of Infection

• Dr. Mohamed El Bashaar

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Causative Agent
Susceptible Host
Reservoir
Portal of Exit
Portal of Entry
Mode of Transmission
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CAUSATIVE AGENTS

• A biologic agent/s capable of causing infectious
  diseases.
• Bacteria,Parasites, Fungi Viruses

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Reservoir

• Place in which an infectious agent can survive
  but may or may not multiply
• Salmonella in milk survives and multiplies
• Hepatitis B virus on surface of hemodialysis
  machine survives but does not multiply.

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Two Major Types of Human Reservoir

• Cases(Patients)
• Acute clinical
• Subclinical
• Carrier (HBV,HIV)

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Portal of Exit Associated w/ Human Reservoirs

• Respiratory Tract
• Genitourinary Tract
• Gastrointestinal Tract
• Skin/Mucous Membrane
• Transplacental (mother to fetus)
• Blood

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Modes of Transmission

• The mechanism for transfer of an infectious agent
  from a reservoir to a susceptible host.

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Means of TransmissionFive Main Routes

• Droplet
• Airborne
• Common Vehicle (Food, blood)
• Vector-borne
• Contact
• Direct Contact
• Indirect Contact (Objects)

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Portal of Entry

• The path by which an infectious agent enters the
  susceptible host
• Respiratory tract
• Genitourinary tract
• Gastrointestinal tract
• Skin/mucous membrane
• Transplacental (fetus from mother)
• Parenteral (percutaneous, via blood)

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Susceptible Host

• A person usually lacking effective resistance to
  a particular pathogenic agent.

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Sources and modes of transmission of infection

• Person-to-Person Spread
• Skin-to-skin contact, clothes, (folliculitis with
  Staphylococci or MRSA ,viral as HSV1)
• Droplets during coughing, sneezing (common cold,
  flu, swine flu, pneumonia, bacterial meningitis),
  or kissing (infectious mononucleosis, cold sores)
• Stool-to-mouth (fecal-oral) spread, usually via
  dirty hands or utensils (hepatitis A, Giardia,
  pinworms(oxyuris), cholera, poliomyelitis)

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• Sexually transmitted (gonorrhea, Chlamydia,
  genital HSV2, genital warts (human papillomavirus
  HPV), AIDS syphilis)
• Blood-to-blood contact by
• contaminated needles, usually by drug addicts or
  health workers (hepatitis B, C, AIDS)
• blood transfusion (hepatitis B,C, AIDS, viral
  hemorrhagic fevers)
• Vectors mosquitoes (Malaria, Dengue fever)

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• Spread from mother to fetus during pregnancy
  (hepatitis B, C, HIV, HSV-1, HSV-2, rubella,
  toxoplasma, varicella, syphilis, bird flu), or
  delivery (Chlamydia trachomatis, Neisseria
  gonorrheae, group B StreptococciS.agalactiae)
• An autoinfection the spread of an infection
  from one body part to another, usually by hands
  or clothes (folliculitis, impetigo).

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• 2. Waterborne Infections
• By drinking contaminated water, one can contract,
  cholera, dysentery, typhoid fever, amebiasis
  cryptosporidium . Tap water in hospitals may
  contain Legionella.
• By swimming in contaminated swimming or spa
  pools, or lakes, intestinal parasite
  Cryptosporidium, eye and middle ear infections.
  Certain parasites may enter through the
  skin(schistosoma).
• Water in public showers may hold Legionella
• Flood water may contain various pathogenic
  microbes

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• 3. Airborne Infections
• Industrial cooling or hot water systems, air
  condition can be a source of M. tuberculosis or
  Legionella
• 4. Soil
• During walking barefoot, Clostridium tetani, or
  intestinal parasites, like Strongyloides
  stercoralis or hookworms(Ancylostoma) can be
  contacted.
• Eating with soil-contaminated hands can also
  result in infection by parasites.

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• 5. Food-Borne Infections
• Food poisoning is an infection of the
  gastrointestinal tract caused by microbes from
  contaminated food bacteria like Salmonella or
  E.coli, toxins from Staphylococcus aureus or
  Clostridium botulinum or viruses like
  Enterovirus.
• .

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• 6. Nosocomial Infections Health-care acquired
  infections(HAI)
• Usually caused by bacteria that are resistant to
  antibiotics (multi-drug resistant strains).
• Urinary tract infections from urinary catheters
  (CA-UTI) .
• Surgical-site infections (SSI).
• Catheter related Blood stream infections(CR-BSI).
• Ventilator associated pneumonia(VAP)
• Fungal infections, in patients with low immunity.