Dr. Greene, how do you tell if a child has an active mycoplasma infection? When is mycoplasma pneumoniae IgG increased and decreased after an infection? How important are mycoplasma infections in children?

Picture a child who for 3 or 4 days feels ill with a fever and perhaps a headache. She doesn't have much of a runny nose, but a cough has developed. The cough has become increasingly prominent even though the fever and other symptoms have gone away. Initially, the cough was dry and nonproductive but begins to produce sputum as the weeks go by. And the weeks do go by--the cough lingers 1, 2, 3, 4 weeks, with no sign of improvement. This little girl has pneumonia caused by Mycoplasma sp. (although because she is acting fairly well, no one has made this diagnosis). Mycoplasmas are the leading cause of pneumonia in school-aged children and adolescents.

Mycoplasmas are the smallest free-living creatures ever discovered. Dwarfed by amebas, they are smaller even than bacteria (or perhaps than "other bacteria"--sometimes they are classified as the smallest bacteria). They are the original "morphers"--changing shape from long, thin filaments to little spheres to intricate branching patterns to bulbs to an endless variety of asymmetric shapes, like the latest science-fiction special effects. They grow and reproduce very slowly for such tiny organisms.

Almost 100 species of mycoplasmas have been identified and are plentiful everywhere in nature. Fifteen species are known to live in humans, most as normal and helpful intimate neighbors. The species you asked about, Mycoplasma pneumoniae, is a very common cause of human disease.

Many pediatricians still consider mycoplasmas an uncommon cause of disease. Infectious diseases are often identified by "culturing" them--taking a small sample of tissue or fluid and keeping it in an incubator for a while to see what grows. Mycoplasmas are very tiny, shape-shifting, slow-growing critters that don't often show up on cultures.

But newer, more sensitive antibody tests prove mycoplasmas to be a common cause of infection. Over 40% of children have had a mycoplasma infection by their first birthday, more than 65% by age 5 years, and 97% by adulthood. Repeat infections, even severe repeat infections, are common (Textbook of Pediatric Infectious Diseases, WB Saunders, 1998, pp 2259--2286).

In addition to pneumonia, mycoplasmas can cause a variety of other respiratory illnesses, including ear infections (about 12% of all ear infections), sinus infections, bronchitis, croup, bronchiolitis, severe sore throats, infectious asthma, and even a version of the common cold. Most mycoplasma infections are not very severe but last for quite a long time.

About 25% of kids with mycoplasma infections have nausea, vomiting, or diarrhea. Uncommonly, mycoplasmas can cause hepatitis, pancreatitis, arthritis, heart disease, anemia, or neurologic disease.

Most of the commonly prescribed antibiotics are completely ineffective against mycoplasma infections.