Mycoplasma pneumoniae is a type of bacteria. It often causes a mild illness in older children and young adults, but it can also cause pneumonia, an infection of the lung.

The bacteria usually cause an upper respiratory tract infection with a cough and sore throat.

Most illnesses that come from Mycoplasma pneumoniae (M. pneumoniae) are mild. For this reason, doctors sometimes call them "walking pneumonia."

According to the Centers for Disease Control and Prevention (CDC), the bacteria are responsible for the common "chest cold," or tracheobronchitis, in children.

If a person has any signs of infection, they should seek medical attention.

M. pneumoniae is usually a community-acquired infection. A study published in 2015 suggested that is responsible for 10 to 40 percent of all cases develop outside hospitals or clinics.

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M. pneumoniae is a common cause of respiratory infection in young people.

M. pneumoniae infection is most likely to affect young adults and older children. Other high-risk groups include older adults and people with a weakened immune system.

Outbreaks can occur in places where groups of people mix closely, such as schools and nursing homes.

M. pneumoniae spreads more slowly than other respiratory diseases, but it can affect people within the same household.

The infection spreads when droplets containing the bacteria travel through the air when a person coughs or sneezes.

This can only happen when people are in close contact, because M. pneumoniae dries out easily. It can only survive in water droplets.

However, once the bacteria enter the upper airways, they are difficult to remove from the body.

Special adaptations enable them to stick to cells. This is how they cause damage and trigger a fight with the immune system, creating the symptoms of illness.

Most cases of M. pneumoniae infection last in a mild form for several weeks.

The symptoms usually take between 1 and 4 weeks to appear, according to the CDC. The typical symptoms are those of a chest cold:

  • a sore throat
  • feeling tired
  • a fever
  • a cough that gradually gets worse
  • a headache

The symptoms of M. pneumoniae infection are similar to those of other respiratory infections. Its key feature is a lasting cough.

When infection occurs deeper in the lung, more severe symptoms can result.

These can include:

  • difficulty breathing
  • rapid, shallow breathing
  • wheezing
  • chest pain that feels worse when a person breathes or coughs
  • raised heart rate
  • sweating and shivering
  • a loss of appetites
  • malaise, or a general feeling of being unwell

A person with asthma may find that infection with M. pneumoniae makes their symptoms worse.

Complications of M. pneumoniae are rare, but they can affect people who already have a lung disease, such as asthma or chronic obstructive pulmonary disease (COPD).

People will have a higher risk of complications if they:

  • are over 65 years old
  • have a weakened immune system

People should see their doctor each time they get an infection if:

  • they already have a long-term condition
  • a doctor has told them that they might be more vulnerable to illness

Sometimes, symptoms can affect other parts of the body, not only the lungs.

This can lead to life-threatening neurological diseases, such as encephalitis, as well as dermatologic disease, hemolytic anemia, and arrhythmias, among others.

Anyone who has symptoms that make breathing difficult should see a doctor as soon as possible. If complications occur, hospitalization may be necessary.

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The doctor will carry out physical examination to find out if the person has an infection.

A doctor will ask the person about their medical history, any symptoms, and when these first started.

They will also carry out a physical examination, including listening to the chest and examining the person's throat. If symptoms are severe, they may request an X-ray.

The symptoms of M. pneumoniae infection can be more subtle than those of other forms of lung infection. For example, the doctor may not hear any unusual sound from the lungs. This can make it harder to diagnose.

In addition, since M. pneumoniae has similar symptoms to other conditions, it can be hard to identify. The doctor will need to rule out other conditions.

A clear diagnosis might only be possible if the symptoms do not respond to the usual treatments for upper respiratory infections, which involve other types of bacteria.

Lab tests

Doctors do not usually recommend lab tests for a mild pneumonia infection, as they can be unreliable, expensive, not widely available, or take a long time.

However, if the symptoms suggest that there may be a more serious infection, lab tests are an option. They can sometimes show which kind of microbe is present. Knowing this helps the doctor to decide which kind of drug treatment the infection might respond to.

To do the test, the doctor will take a sputum sample, a swab of the throat, or a wash from the upper tubes of the lung.

A blood test can find signs that an infection is present by looking for antibodies.

Most cases of M. pneumoniae upper airway infection do not need any drug treatment. The infection will run its course without causing serious problems.

The person usually returns to full health after a number of weeks, although the cough may last longer.

The doctor will normally recommend:

  • resting at home when feeling unwell
  • drinking plenty of fluids
  • taking over-the-counter pain relief for a headache or a sore throat

Antibiotic use

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If a doctor prescribes antibiotics, it is important to follow the instructions exactly.

It can be hard to distinguish between the more common types of pneumonia infection and that which comes from M. pneumonia.

Some types are viral or fungal, and they will not respond to antibiotics. However, after diagnosing pneumonia, most doctors will treat it with a carefully selected antibiotic.

Macrolide antibiotics can be effective in treating an infection caused by M. pneumoniae, but they will not work for everyone. Research shows that resistance to macrolides is growing. In the United States, up to 10 percent of cases of M. pneumoniae may be resistant to these drugs.

If macrolides do not work, the doctor may recommend other antibiotics, such as fluoroquinolones or tetracyclines.

To ensure that the antibiotic works, the person must take the full course, exactly as the doctor recommends.

Sometimes people stop taking antibiotics when their symptoms go away, but the infection can return later, because traces of the bacteria remain.

Treating complications

If complications arise, the person will receive treatment for these, too.

Intensive hospital treatment may be necessary if a person's blood pressure is low or they need help with breathing.

As with other upper respiratory tract infections, coughing can spread the bacteria to other people.

For this reason, people should avoid close contact with others if they have the infection or feel unwell and have a cough.

Influenza, H. influenzae, varicella, and pneumococcal vaccinations can help protect people who are at risk of community-acquired pneumonia.

The following groups should receive the pneumococcal vaccine:

  • those who are susceptible to this type of infection
  • people with an existing heart or lung condition
  • people with an immune disorder
  • those who smoke

The type of vaccination depends on the age group. A doctor can advise about this.

M. pneumoniae causes a relatively common and fairly mild respiratory tract infection. The person usually returns to full health without treatment.

However, a person with any sign of infection should seek medical advice, because sometimes complications can arise.