Atypical pneumonia is usually caused by certain bacteria such as mycoplasma pneumoniae, chlamydophila pneumoniae and legionella pneumophila. Mostly atypical pneumonia is milder form of pneumonia; however, pneumonia caused by legionella, in particular, can cause acute case that can also lead to high mortality rate.
Atypical pneumonia, unfortunately, does not respond to the usual antibiotic treatment. Though it is caused by bacteria (mycoplasma pneumoniae, chlamydia pneumoniae, legionella pneumophila and bordatella pertussis), viruses like influenza and coronaviruses are known to cause atypical pneumonia. Normally, this type of infection is not as severe as the conventional pneumonia, but legionnaire disease (legionella pneumophila) kills up to 50% of its victims if left untreated. The deadly SARS virus, which made its presence felt only recently, is a new coronavirus that causes atypical pneumonia.
Atypical pneumonia (mycoplasma and chlamydophila) are mild and are characterized by a more drawn out course of symptoms. Mycoplasma pneumonia often affects young people and it has symptoms that are usually outside of the lungs. Some of the symptoms are anemia and rashes, and neurological syndromes such as meningitis, myelitis, and encephalitis. The severe forms of mycoplasma pneumonia have been seen in all age groups. Chlamydophila pneumonia occurs throughout the year and contributes to 5-15% of all pneumonia cases. It is a milder form of pneumonia with a low mortality rate. In contrast, atypical pneumonia caused by legionella accounts for 2-6% of the total pneumonia cases and has a higher mortality rate. Elderly individuals who have underlying diseases, smokers, and people with chronic illnesses and immunocompromised people are at higher risk of contracting this type of pneumonia. Pneumonia due to legionella can also be contracted through contact with contaminated aerosol systems like infected air-conditioning systems.
The probability of contracting atypical pneumonia depends on the patient and the patient’s environment. For instance, chlamydia and mycoplasma pneumonias are spread by close contact in places that are crowded like military barracks or college dormitories. Chronic illnesses, especially respiratory illnesses (i.e. bronchitis, emphysema, COPD), and a history of smoking are other factors that predispose individuals to atypical pneumonias. Use of chronic immunosuppressants like steroids is known to make people more susceptible to the infection.
The best method to treat atypical pneumonia is antibiotic therapy. Mild cases can be treated at home by administering oral antibiotics. However, severe cases, especially the ones caused by legionella may need one to take intravenous antibiotics and oxygen supplementation. Antibiotics that are known to be active against these organisms include – erythromycin, clarithromycin, azithromycin, fluoroquinolones and their derivatives (such as levofloxacin), and tetracyclines (such as doxycycline).
Atypical pneumonia caused by Mycoplasma and Chlamydophila usually result in milder forms of pneumonia and are typified by a more drawn out course of symptoms unlike other forms, which come on quicker and with more severe early symptoms.
Younger people are more likely to be affected by mycoplasma pneumonia and may develop symptoms outside of the lungs (eg anemia and rashes), and neurological syndromes (such as meningitis, myelitis and encephalitis). However, more severe forms of pneumonia have been found to affect all age groups.
Occuring all year round, Chlamdophila pneumonia accounts for 5-15% of all pneumonias. It is a mild form and with a low mortality rate. On the other hand, atypical pneumonia due to Legionella has a higher mortality rate and accounts for 2-6% of all pneumonias.
Those falling in the high risk category for this kind of pneumonia are elderly individuals, smokers, people with weakened immune systems and those with chronic illness. Contact with contaminated aerosol systems (eg infected air conditioning) is also responsible for causing pneumonia due to Legionella.
Factors that could be responsible to increase the risk of atypical pneumonia in infants include :
A wide range of respiratory infections including tracheobronchitis, pneumonia and upper respiratory tract infections are caused by mycoplasma pneumonia. It has been observed that only 3 to 10 percent of persons affected with mycoplasma pneumonia develop pneumonia. As atypical pneumonia becomes more common with advancing age, it is important to ascertain and diagnose this infection in elderly patients.
Atypical pneumoniae infection occurs throughout the year but can cause periodic outbreaks within small communities. Transmission is by person-to-person contact, and infection spreads slowly, most often within closed populations (e.g., households, schools, businesses).
The normal clinical course of pneumonia due to mycoplasma pneumoniae is mild and self contained. The mortality rate is about 1.4%. However significant pulmonary complications like effusion, empyema, pneumothrax and respiratory distress syndrome could develop.
Atypical pneumonia could also result in several extrapulmonary ailments. Some skin infections thus caused include erythema multiforme, erythema nodosum, maculopapular and vesicular eruptions, and urticaria. Neurologic derangements like aseptic meningitis, cerebral ataxia, Guillain Barre syndrome, encephalitis and transverse myelitis. When mycoplasma pneomoniae titers are high, the production of cold agglutinins can result in hemolytic anemia. Further complications like myocarditis, periicarditis, pancreatitis and polyarthritis can also develop.
Atypical pneumonia usually caused by mycoplasma and chlamydophila bacteria is a milder form of pneumonia. Legionella bacteria can cause a severe case of atypical pneumonia. The atypical pneumonia symptoms are as follows:
Recent studies have raised more questions about the appropriateness of the term “atypical pneumonia” One study by Lieberman and associates from Israel observed 346 patients. Most of the tests conducted were serologic and several causative agents were identified in 133 (38.4%) of the patients. The tests revealed that the second most frequent infection was caused by the mycoplasma pneumonia organism.
Infections are often caused by multiple agents. Therefore it doesn’t really matter which agent has brought on the infection in cases of community-acquired pneumonia. To what extent may an M pneumoniae or C pneumoniae infection could predispose the patient to a second infection can be easily observed by their pathologic effect on ciliated epithelium. Both the infections could cause ciliopstasis which could increase the susceptibility of the patient to the other more virulent pathogen forms such as S pneumoniae.
An interesting report by Lieberman and associates concluded that in two thirds of the patients infected with pneumonia caused by multiple agents, the severity of illness was not different from those infected by a single pathogen identified as M pneumoniae.
The academic opinion on whether patients infected with a single pathogen need to be treated differently, greatly varies. It is advisable that treatment decisions should be made empirically because it may be possible that no reliable clues are obtained at the time of diagnosis.
A recent meta-analysis clearly questions the validity of the usefulness of the time-honored Gram’s stain. However, as implied by the recent community acquired pneumonia guidelines stipulated by the infectious Disease Society of America, this view is not shared by some investigators. They suggest that Gram’s stain is not really useful and should not be relied upon to decide whether or not to limit broad spectrum therapy. It is advisable that until rapid diagnostic tests using molecular techniques become available, community acquired pneumonia should be treated empirically, based on clinical and radiographic observations.
In such a situation, the severity of the illness would determine its treatment. Young patients with no serious complications and without any real need to be hospitalized could remain outpatients and be treated with the newer macrolide or with doxycycline. but if the patient is hospitalized due to the severity of illness and the presence of other serious complications, it has to be determined which infection requires to be treated first. In most cases, infections due to S pneumoniae need to be treated first. Also, appropriate therapy for L pneumophila would also be needed to minimize the risk of infection caused by mycoplasma and Chlamydia organisms.
The method of treatment depends on the presence of beta-lactam-resistant S pneumoniae is present in the individual community. As the incidence of such organisms is on the rise, the traditionally approved combination of a beta-lactam and a macrolide is surely going to be replaced by the use of fluoroquinolones. According to present trends the latter therapy is preferred for hospitalized patients.