Mycoplasma pneumoniae is a pathogenic microorganism that infects people and can be tested for antibodies to Mycoplasma pneumoniae through a blood test, which can be positive or weakly positive for the corresponding IgM antibody. A weak positive test indicates that the person is likely to be infected with Mycoplasma pneumoniae and is considered to be infectious, regardless of whether there are obvious symptoms. Some Mycoplasma pneumoniae infections in people can lead to obvious manifestations of pneumonia or bronchitis such as cough and fever, or upper respiratory tract infections, and they are all infectious. Some people who are infected with Mycoplasma pneumoniae may not have any symptoms, and are then insidiously infected, but are in fact also infectious. However, a weakly positive IgM antibody to Mycoplasma pneumoniae is not enough to identify Mycoplasma pneumoniae infection by itself, because sometimes people who are not infected with Mycoplasma pneumoniae may also have a weakly positive IgM antibody. The presence of Mycoplasma pneumoniae infection can only be determined clinically if the IgM antibody titer is high or if there is a fourfold or higher increase in the course of the disease. Therefore, a weakly positive qualitative test alone does not specifically confirm the presence of Mycoplasma pneumoniae infection.