Mycoplasma pneumoniae is a common cause of upper and lower respiratory tract infections. It remains one of the most frequent causes of atypical pneumonia particularly among young adults.[1,2,3,4,5] Although it is highly transmissible, most infections caused by this organism are relatively minor and include pharyngitis, tracheobronchitis, bronchiolitis, and croup with one fifth of infections being asymptomatic.[6,7] Only 3 -10% of infected subjects develop symptoms consistent with bronchopneumonia and mortality from infection is rare.[6,7] The organism is fastidious and difficult to grow on cultures. Therefore, diagnosis of infections caused by this organism is usually confirmed with serological tests or polymerase chain reaction-gene amplification techniques. At King Abdulaziz University Hospital (KAUH), Jeddah, Saudi Arabia, the facility to perform Mycoplasma culture has been available since January 1997. As published information concerning M. pneumoniae infections in Saudi Arabia is scarce,[8,9,10] we wished to study the epidemiology and clinical features of culture-proven infections caused by this organism at this hospital.

The Statistical Package for Social Sciences (SPSS) program was used for data analysis. Comparison of categorical data was by Chi-square statistic or Fisher's exact test for small expected values.

Mycoplasma pneumoniae is one of the most common causes of atypical pneumonia accounting for 5-23% of community-acquired pneumonia,[1,2,3,4,5] In a study of 511 children with acute respiratory tract infection in Riyadh, Saudi Arabia, Mycoplasma pneumoniae was found to be the second most common causative agent after Respiratory syncytial virus (RSV) accounting for 9% of all cases,[8] In a study of 112 adult patients with community acquired pneumonia admitted to a military hospital in Riyadh, Saudi Arabia, this organism accounted for 6% of all cases,[9] In another retrospective study of 567 pneumonic episodes in adult patients from Al-Qassim area, the organism accounted for 23% of all episodes,[10] The organism also causes other relatively minor infections such as pharyngitis, tracheobronchitis, bronchiolitis, and croup. It is transmitted from person-to-person by infected respiratory droplets during close contact. It is most common in school-aged children, military recruits, and college students.[11] Most cases occur singly or as family outbreaks. Larger outbreaks can also occur in closed populations such as military recruit camps or boarding schools,[12] Infection occurs most frequently during the fall and winter in temperate climates but may develop year-round,[13] The average incubation period is 3 weeks following exposure,[6] Although rare, complications are protean and may involve virtually any organ system such as the respiratory system (e.g.: pleurisy, pneumothorax, acute respiratory distress syndrome, lung abscess), the hematologic system (e.g.: hemolytic anemia, intravascular coagulation, thrombocytopenia), the dermatologic system (e.g.: maculopapular or urticarial rashes, erythema multiforme, erythema nodosum), the musculoskeletal system (e.g.: myalgias, arthralgias, arthritis), the cardiovascular system (e.g.: pericarditis, myocarditis), the nervous system (e.g.: meningoencephalitis, Guillain-Barre syndrome, neuropathies, acute psychosis), or the eye (optic disc edema, optic nerve atrophy, retinal exudation and hemorrhages).[6,7,14,15,16,17,18] Immunity following infection is not long lasting.[11]

In our study, the infection affected all age groups but was most common in infants (32.5%) and preschool children (22.5%), and least common in adults aged 15 to 30 years (2.5%) and elderly above 70 years of age (5%). This contrasts with data from temperate countries where the infection is most common in school-aged children, and young adults.[11] One possible explanation for this difference is that infants and preschool children perhaps had more severe infections than did school-aged children, and young adults which prompted presentation of the former group to the hospital. The infection occurred year-round but was most common in the fall (35%), and spring (30%), and least common in the summer (10%). Most infections were community-acquired (92.5%).

More than one half of patients (57.5%) presented with pneumonia, and about a third (27.5%) presented with upper respiratory tract infection, Immunocompromised patients and patients 60 years of age or older were more likely to present with pneumonia as opposed to upper respiratory tract infection than non-immunocompromised patients or those below 60 years of age. Cough (82.5%), fever (75%), and malaise (58.8%) were the most common presenting symptoms. Cough was usually dry or slightly productive of white sputum and mild to moderate in severity. Most febrile patients had mild to moderate fever of 39°C or less; high-grade fever of more than 39°C was rare. Crepitations (60%), and wheezes (40%) were the most common signs. Wheezes were as common in patients with no history of obstructive airway disease (9 patients) as it was in those with such a history (7 patients). Bronchial breathing as a sign of consolidation was detected in only one fourth of patients with pneumonia, which is consistent with the known disparity between clinical and radiological signs of M pneumoniae pneumonia. Crepitations, however, were detected in the majority (79.2%) of patients. Pleuritic chest pain and pleural effusion were rare.

More than half (56.5%) of the patients with pneumonia had uneventful recovery. Mortality from M. pneumoniae pneumonia was high (12.5%) and occurred only in patients with underlying comorbidities. None of the 9 patients with no underlying comorbidities died of M pneumoniae pneumonia. The relatively high complications rate (16.7%) and mortality (12.5%) related to M. pneumoniae pneumonia are likely due to selection bias as most patients with pneumonia were sick enough to require admission to the hospital (21/24 or 87.5%) and most of them had comorbidities (20/24 or 83.3%).

In conclusion, our data shed some light on the epidemiology and clinical features of M pneumoniae infections in one of the Saudi tertiary care centers. The data are comparable to those of other countries except for the finding that infections were more common in infants and preschool children than in school children and young adults. Additionally, mortality attributable to M. pneumoniae pneumonia was relatively high in patients with comorbidities. It is hoped this information will assist clinicians in their approach and management of respiratory tract infections.