If you suspect giardiasis, call your doctor immediately if:

• Diarrhea is black or bloody. Note: Medicines containing bismuth (such as Pepto-Bismol) can turn stools black, but this is not harmful.
• Signs of severe dehydration appear. These include:
  • Little or no urine (or wet diapers) for 8 hours, or fewer than 3 urinations (or wet diapers) in 24 hours, usually with one or more of the other signs of dehydration listed below.
  • Doughy skin that doesn't bounce back when pinched.
  • Difficult or slow response or confusion.
  • Sunken eyes.
  • Sunken soft spot (fontanel) on an infant's head.
  • Low blood pressure.
  • Dizziness, especially if you feel dizzy when you stand up or change position suddenly.

Call within a day if you have:

• Belly pain along with diarrhea, and the pain is not relieved by passing stools or gas.
• Diarrhea along with a fever of 101 F or higher with chills, vomiting, or fainting (not just lightheadedness).
• Severe diarrhea (many watery stools in a person who also seems very sick) that lasts longer than:
  • 2 days in an adult.
  • 1 to 2 days in a child younger than 4.
  • 8 hours in an infant 3 to 6 months old.
  • 4 hours in an infant younger than 3 months.

Call a doctor if:

• Diarrhea develops and persists after you have swallowed untreated water.
• Mild to moderate diarrhea (a few stools that are looser than normal without other signs of illness) lasts longer than 4 to 7 days in a child.
• Diarrhea continues without obvious cause for more than 1 to 2 weeks.
• An infant or child is not developing or gaining weight as expected (failure to thrive).

Watchful Waiting

Most cases of diarrhea are caused by a viral infection and improve with a few days of home care. But if diarrhea is severe or lasts longer than a week or so, or if the above symptoms are present, call your doctor for advice.

Who To See

The following health professionals will be able to diagnose and treat giardiasis:

• Family medicine physician
• Pediatrician
• Internist
• Physician assistant
• Nurse practitioner

Referral to a gastroenterologist usually is not necessary unless symptoms are persistent or severe.

To prepare for your appointment, see the topic Making the Most of Your Appointment