Incubation Periods of Childhood Diseases

In infectious disease terms, the incubation period is the amount of time between being exposed to a contagious disease and developing symptoms.

Depending on the disease, the incubation period can be just a few hours or can last for several months. Knowing the incubation period for a disease can help you understand if your child is still at risk of getting sick or if he is in the clear — whether he is exposed to someone with strep throat, measles, or the flu.

It can also help you figure out where and when your child got sick. For example, if your infant develops chickenpox, a vaccine-preventable disease, you can't blame it on your cousin who doesn't vaccinate her kids and who was visiting just three days ago. The incubation period for chickenpox is at least 10 to 21 days. So your child who is too young to be vaccinated likely caught chicken pox from someone he was exposed to a few weeks ago.

As we have seen in outbreaks of Ebola and measles, a disease's incubation period can also help you figure out how long an exposed person needs to stay in quarantine. After all, if they don't get sick once the incubation period is over, then they likely won't get sick and can be released from quarantine.

The incubation period for some common diseases includes:

• Adenovirus - 2 to 14 days, leading to a sore throat, fever, and pink eye
• Vomiting after exposure to Bacillus cereus, a type of food poisoning - 30 minutes to 6 hours (very short incubation period)
• Clostridium tetani (Tetanus) - 3 to 21 days
• Chickenpox - 10 to 21 days
• Coxsackievirus infections, such as HFMD - 3 to 6 days
• Epstein-Barr Virus Infections (Infectious Mononucleosis) - 30 to 50 days (long incubation period)
• E. coli - 10 hours to 6 days (short incubation period)
• E. coli O157:H7 - 1 to 8 days
• Fifth disease - 4 to 21 days, with the classic 'slapped cheek' rash
• Group A streptococcal (GAS) infection (strep throat) - 2 to 5 days
• Group A streptococcal (GAS) infection (impetigo) - 7 to 10 days
• Head lice (time for eggs to hatch) - 7 to 12 days
• Herpes (cold sores) - 2 to 14 days
• Influenza (flu) - 1 to 4 days
• Listeria monocytogenes (Listeriosis) - 1 day to 3 weeks, but can be as long as 2 months (long incubation period)
• Measles - 7 to 18 days
• Molluscum contagiosum - 2 weeks to 6 months (long incubation period)
• Mycobacterium tuberculosis (TB) - 2 to 10 weeks (long incubation period)
• Mycoplasma penumoniae (walking pneumonia) - 1 to 4 weeks
• Norovirus ( the 'cruise ship' diarrhea virus) - 12 to 48 hours (very short incubation period)
• Pinworms - 1 to 2 months
• Rabies - 4 to 6 weeks, but can last years (very long incubation period)
• Respiratory Syncytial Virus (RSV) - 2 to 8 days
• Rhinovirus (common cold) - 2 to 3 days, but may be up to 7 days
• Roseola - about 9 to 10 days, leading to a few days of fever and then the classic rash once the fever breaks
• Rotavirus - 1 to 3 days
• Gastrointestinal symptoms (diarrhea and vomiting) after exposure to Salmonella - 6 to 72 hours
• Scabies - 4 to 6 weeks
• Staphylococcus aureus - varies
• Streptococcus pneumoniae (can cause pneumonia, meningitis, ear infections, and sinus infection, setc.) - 1 to 3 days
• Whooping ​cough (pertussis) - 5 to 21 days

Knowing the incubation period of an illness isn't always as helpful as it seems, though, as kids often have multiple exposures when kids around them are sick, especially if they are in school or daycare.

Conditions with long incubation periods can also fool you, as you might suspect a recent exposure, but it was really someone your child was around months ago.