Mycoplasma infection in children and adolescents
Mycoplasma pneumoniae is one of the leading causes of community-acquired pneumonia in school-aged children, adolescents and young adults. The infection easily spreads in closed groups: schools, boarding schools, military units, and often gives rise to group outbreaks, when several people in one class fall ill in succession.
The clinical picture is typical of atypical pneumonia: gradual onset, sore throat, prolonged dry cough, moderate fever, headache and weakness. The cough may persist for weeks after the temperature returns to normal. Sometimes extrapulmonary manifestations are added - rash, joint pain, hemolytic anemia.
IgG antibodies appear later than IgM, after about three to four weeks, and persist for a long time. A single positive result more often reflects a previous infection, and a significant increase in titer in two samples taken at an interval of two to three weeks is considered evidence of the current episode. To quickly confirm the diagnosis in the acute period, PCR of a nasopharyngeal smear is preferable.
What do IgM and IgG mean?
The immune system produces different classes of antibodies at different times. Immunoglobulins M appear first, usually in the first or second week after infection, last for several weeks or months and then disappear. Their detection indicates an acute or recent process.
Immunoglobulins G appear later, after a few weeks, and persist for years, and often for life. They mean that a meeting with the pathogen took place in the past, and in many cases indicate formed immunity. Therefore, positive IgG in itself is not a reason for treatment.
Why dynamics are important, not just a number
A single result is often ambiguous. Antibody levels vary from person to person, with borderline levels falling into what is known as a gray area. A reliable sign of active infection is a fourfold increase in IgG titer in paired sera taken at intervals of 10–14 days.
This is why serology is rarely prescribed as a single test. The doctor either combines IgM and IgG, or repeats the test, or confirms the result with a direct method - PCR, which detects the DNA or RNA of the pathogen itself.
Limitations of the method
Antibodies do not appear immediately: in the first days of the disease, serology can be negative if the infection has already begun - this is the period of the serological window. In case of immunodeficiency and against the background of immunosuppressive therapy, antibodies may not be produced at all.
Cross-reactions with related pathogens are also possible, giving a false-positive result. Therefore, treatment is never prescribed “based on analysis” - only on the basis of a combination of clinical data and research results.