Walking pneumonia is a clinical diagnosis  for a dry, persistent, hacking cough. The cough occurs both day and night and is sometimes accompanied by a low-grade fever and low-grade headache.
In young children (3-10 yrs) the walking pneumonia germs often manifest as a hacky bronchitis (inflammation of the bronchial tubes) and not pneumonia (lung infection). They will not be visibly “sick” and usually continue going to school every day – hence the name “walking” pneumonia to differentiate the illness from the far more severe “galloping” pneumonia.
If a child’s bronchial cough is contagious and passed to an adult, it can develop into a pneumonia. This infection can take about 3 weeks to resolve. [An X-ray done at the onset of an adult’s “walking pneumonia” shows the lungs to be clear; a couple of weeks later, as the cough is improving, an X-Ray will show diffuse white streaks.]
“Walking pneumonia” is the result of infection by one or several of three contagious pathogens, or bacteria: Mycoplasm pneumoniae, Chlamydia pneumonia, and Bordella pertussis. Environmental pathogens also play a role, and include aspergillosis and legionella.
Mycoplasm pneumoniae is a small, ubiquitous bacteria. It is transmitted from person to person through close interaction, most frequently during the fall and winter. Infection by M. pneumoniae can intensify or worsen asthma symptoms, or induce wheezing in children not diagnosed with asthma, but only occasionally causes pneumonia.
Chlamydia pneumonia is a less common bacteria than M. pneumonia, and does not cause severe illness in most people. Elderly adults and people with sickle-cell disease are among those most commonly infected.
Bordella parapertussis is a variant species of the bacteria Bordella pertussis. While infection by B. pertussis can cause the severe and highly contagious pertussis, or “whooping cough,” B. parapertussis brings on only an extremely mild variant of the cough. People who have been vaccinated against B. pertussis can still get a hacky cough if exposed to B. parapertussis in the environment (See the article on Pertussis).
There are several ‘walking pneumonia’ pathogens that are acquired from the home, office or great outdoors. An example of this is aspergillosis, a mold that can be found in water damaged buildings, in dirt, and the underside of fallen leaves in the autumn. If a person is raking a pile of leaves, or cleaning up a flooded basement, he/she can inhale a concentration of aspergillosis particles. If the person has a normal mucosal defense system, they will not get sick. However, if they have a viral illness, a compromised immune system, OR if they inhale a very large amount, they can develop a hacky cough or wheezing.
Legionella is a less common environmental pathogen, and has little to no effect on the vast majority of people. It can live in standing water and contaminate air conditioner systems, humidifiers and infrequently used water pipes. In vacation houses and pool showers, for instance, water pipes that are turned off for periods of time can become harbors for legionella .
If the doctor suspects one of the walking pneumonia germs, he/she will prescribe a macrolide antibiotic such as Zithromax or Biaxin. The antibiotics speed recovery and render the patient uncontagious to others. Treatment will also calm some of the non-pulmonary symptoms that can be triggered by the illness. The walking pneumonia infection creates high molecular weight immune complexes that can make the patient feel achy and headachy, and experience tingling of their feet, especially when exposed to cold. It is usually very difficult and expensive to test for the exact bacteria infecting a patient. In certain circumstances specialized tests are done, but the patient often will have recovered by the time the results come back.
The Bottom Line
The natural course of walking pneumonia in the vast majority of children is complete recovery after several weeks. However, adults and people with underlying medical conditions can be infected by a child’s cough.
 Healthcare providers make a clinical diagnosis, a presumption that a certain disease or condition is the cause of illness, based on observation of classic symptoms without “hard” evidence (lab screening results, X-rays, etc.).
 Note: People with suppressed or weakened immune systems, such as cancer patients undergoing chemotherapy, should be careful taking showers, as legionella can be in the shower heads. As the shower is turned on, the germ can be aerosolized and inhaled. To avoid exposure, these patients should take baths, and their hot water thermostat should be kept above 125 degrees – a temperature above which people with young children are asked to keep their hot water thermostat. Also, the bathroom should be “aired” out before the patient is allowed into the bathroom so that any possible legionella is diluted.