eMedicine Specialties > Infectious Diseases > Bacterial Infections

Mycoplasma Infections

Author: Ken B Waites, MD, Director of Clinical Microbiology, Professor, Department of Pathology, Division of Laboratory Medicine, University of Alabama at Birmingham
Contributor Information and Disclosures

Updated: Mar 26, 2008

Introduction

Background

Mycoplasma species are the smallest free-living organisms. These organisms are unique among prokaryotes in that they lack a cell wall, a feature largely responsible for their biologic properties such as their lack of a reaction to Gram stain and their lack of susceptibility to many commonly prescribed antimicrobial agents, including beta-lactams. Mycoplasmal organisms are usually associated with mucosal surfaces, residing extracellularly in the respiratory and urogenital tracts. They rarely penetrate the submucosa, except in the case of immunosuppression or instrumentation, when they may invade the bloodstream and disseminate to different organs and tissues throughout the body.

Although scientists have isolated at least 17 species of Mycoplasma from humans, 4 types of organisms are responsible for most clinically significant infections that may come to the attention of practicing physicians. These species are Mycoplasma pneumoniae, Mycoplasma hominis, Mycoplasma genitalium, and Ureaplasma species. The focus of this article is infections caused by M pneumoniae; articles on Ureaplasma infections (eg, Ureaplasma Infection) and genital mycoplasmal infections contain discussions of infections caused by other mycoplasmal species.

Pathophysiology

M pneumoniae is perhaps best known as the cause of walking or atypical pneumonia, but the most frequent clinical syndrome caused by this organism actually is tracheobronchitis or bronchiolitis, often accompanied by upper respiratory tract manifestations. Pneumonia develops in only 5-10% of persons who are infected. Acute pharyngitis and myringitis are less common.

After inhalation of respiratory aerosols, the organism attaches to host cells in the respiratory tract. The P1 adhesin and other accessory proteins mediate attachment, followed by induction of ciliostasis, local inflammation that consists primarily of perivascular and peribronchial infiltration of mononuclear leukocytes, and tissue destruction that may be mediated by liberation of peroxides. The organism also has the ability to exist intracellularly.¹ Additionally, acute mycoplasmal respiratory tract infection may be associated with exacerbations of chronic bronchitis and asthma.²

Spread of infection throughout households is common, although person-to-person transmission is slower than for many other common bacterial respiratory tract infections; close contact appears necessary. Generally, the incubation period is 2-3 weeks. The organism may persist in the respiratory tract for several months, and sometimes for years in patients who are immunosuppressed, after initial infection.³

For additional information on pneumonia, see Medscape's Pneumonia Resource Center.

Frequency

United States

Researchers estimate that more than 2 million cases of M pneumoniae infections occur annually. M pneumoniae causes approximately 20% of community-acquired pneumonias that require hospitalization and probably an even greater proportion of those that do not require hospitalization. M pneumoniae may exist endemically in large urban areas. Epidemics occur every 3-7 years, with the incidence varying considerably from year to year. Disease tends to not be seasonal, except for a slight increase in late summer and early fall.¹

International

M pneumoniae infections occur both endemically and in cyclic epidemics in Japan and several European countries, similar to what occurs in the United States. Less information is available for tropical or polar countries; however, based on seroprevalence studies, the disease also occurs in these regions, suggesting that climate and geography are not important determinants in the epidemiology of M pneumoniae infections.¹

Mortality/Morbidity

• As the term walking pneumonia implies, the great majority of M pneumoniae respiratory tract infections are mild and self-limited, although administration of antimicrobials hastens clinical resolution. Hospitalization is sometimes necessary, but recovery is almost always complete and without sequelae. Recent studies have indicated that M pneumoniae is second only to Streptococcus pneumoniae as a cause of bacterial pneumonia that requires hospitalization in elderly adults.⁴ Subclinical infections may occur in 20% of adults infected with M pneumoniae, suggesting that some degree of immunity may contribute to the failure of clinical symptoms in some instances.
• Recent evidence suggests that M pneumoniae disease is sometimes much more severe than appreciated, even in otherwise healthy children and adults.² Severe disease is more common in persons with underlying disease or immunosuppression. Children with sickle cell disease and functional asplenia may be at greater risk for severe respiratory tract disease due to M pneumoniae. While reports describe fatal cases of mycoplasmal pneumonia, the overall mortality rate is extremely low, probably less than 0.1%.

Race

• No racial predilection is apparent.

Sex

• Available studies indicate no sexual predilection for M pneumoniae disease.

Age

• M pneumoniae has long been associated with pneumonias in children aged 5-9 years, adolescents, and young adults. Infection is particularly common among college students and military recruits who are likely to live together in close proximity. M pneumoniae may be the most common agent causing bacterial pneumonia in such populations.
• In recent years, M pneumoniae infection has been common in persons older than 65 years, accounting for as much as 15% of community-acquired pneumonia cases in persons in this age group.
• The common misconception that M pneumoniae disease is rare among very young populations and among older adults has led to physician failure to consider the organism in the differential diagnoses of respiratory tract infections in persons in these age groups. Physicians should always consider M pneumoniae as a cause of pneumonia in persons of all ages, including children younger than 5 years. Although M pneumoniae disease in infants is somewhat uncommon, when it is present, it can be severe.⁵

Clinical

History

Typical symptoms can develop and persist over weeks to months and include flulike manifestations.

• Symptoms
  • Generalized aches and pains
  • Fever (usually £ 102°F)
  • Cough - Usually nonproductive
  • Sore throat (nonexudative pharyngitis)
  • Headache/myalgias
  • Chills but not rigors
  • Nasal congestion with coryza
  • Earache
  • General malaise
• In very young children, upper respiratory tract manifestations may predominate, whereas in older children and adults, lower respiratory tract symptoms are more likely.

Physical

Physical findings can be quite variable. Patients typically do not appear toxic or severely ill, but some abnormalities may be apparent in a significant proportion of cases.

• Physical findings
  • Oropharyngeal inflammation
  • Cervical adenopathy - Usually absent
  • Erythematous tympanic membranes
  • Conjunctivitis
  • Maculopapular or urticarial rash
• Chest auscultation in patients with pneumonia may demonstrate localized rhonchi and scattered moist rales, generally involving multiple lobes of the lung and sometimes accompanied by wheezes, with no signs of consolidation, egophony, or bronchial breathing.
• In many persons, chest auscultative and percussive abnormalities are minimal to absent.
• Extrapulmonary manifestations may occur in a minority of persons (see Complications).²

Causes

This is a bacterial infection caused by M pneumoniae.

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