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Incubation periods are one of the many facts that we are expected to learn in medical school. However, I wonder how often they are used in diagnosing an infection because I do not think patients have the best memory of when their symptoms start.

Patients may disregard earlier symptoms which are usually milder. Also, the incubation periods of several organisms are similar. Furthermore, invasion of of an infectious agent does not usually cause a symptom. Thus, it is difficult to even determine the incubation period of the infectious agent.

My question is how often do you rely on the incubation period and what do you do to overcome these challenges?

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Incubation periods of common infections

SKIN:

  • Hand/foot/mouth disease..........3-6 days
  • Measles, chickenpox..............7-21 days
  • Rubella...................................14-23 days
  • Lyme disease(Borrelia)..........3-30 days
  • Scabies.....................................4-6 weeks
  • Warts........................................4 weeks-6 months

RESPIRATORY:

  • Viral:
    • Influenza (Seasonal)......1-4 days
    • Colds, sore throat.............2-6 days
    • Influenza (H1N1)...............4-6 days
    • Cold sores (herpes).........2-12 days
  • Bacterial:
    • Diphtheria, strep throat.....2-5 days
    • Whooping cough..............7-10 days
    • Tuberculosis.....................6-24 days
    • Mycoplasma pneum.......1-4 weeks

GASTROINTESTINAL:

TROPICAL FEVERS:

SEXUALLY TRANSMITTED:

  • Gonorrhea..............................2-5+ days
  • Chlamydia..............................1-3 weeks
  • HIV/AIDS................................2-4 weeks
  • Hepatitis B............................2-5 months

OTHER:

Sources (when not explicitly mentioned): Summit Medical Group, Iowa Department of Public Health


How can knowing incubation periods help?

Sometimes, you can get quite accurate information about the time of exposure and onset of symptoms. Knowing incubation periods may not help you make a diagnosis of exact infection but can help you estimate its possibility. Examples:

1) A person with diarrhea eating out in other place than usual (restaurant/street fast food/open market/travel):

  • 6 hours to 4 days ago: likely bacterial food poisoning
  • 1-2 weeks ago, when travelling (India, South America...): possible parasitic infection (Giardia)

2) A person being in a forest 2 weeks ago and remembering or not being bitten by a tick:

  • Having a single big red "bull's eye" rash: possible Borrelia b. infection (Lyme disease)
  • Having severe headache: possible viral meningoencephalitis

3) A person with high fever travelling in Asia/Africa/South America:

  • 1 week ago: possible yellow or other tropical fever
  • 2-4 weeks ago: possible malaria

4) A teacher with GI symptoms and jaundice camping with school children 1 month ago: possible hepatitis A.

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I find incubation periods useful when trying to decide if some some symptom is, or is not, likely to be related to a suspected illness. For instance I recently had a patient whose child was diagnosed with Parvovirus B19 - slapped cheek disease. It was helpful to be able to tell her that most likely she was out of the window for infection.

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  • Hi there. Thanks for your answer. On Medical Sciences, we much prefer answers supported by references or a literature search, rather than personal anecdotes. I realise the question partly lends itself to anecdotal answers, but please consider providing some references for the utility of incubation periods in the diagnosis of infectious disease. – Chris Dec 7 '19 at 22:26

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