My nephew of 3 years old at first, and later my mother, they have been infected by Mycoplasma pneumoniae. Doctors says that after the treatment, infection has disappeared, that only IgG remains positive. But i don´t know why every time that my nephew get sick my mother too. The worst part goes for the kid because often his lungs are affected. The main question is żIf a reinfection or relapse occurs, IgM will be positive or negative?
With recurrent coughing, one has to think about other conditions like asthma. It would be unusual to have a relapse of mycoplasma. IgM can be used to follow this. If this is a new infection or a relapse, the IgM should be positive. What I don't know is how long the IgM remains positive after an initial infection. My guess would be for 2-4 weeks, based on IgM response in other illnesses. In my six person peds practice in Michgan, we virtually never order mycoplasma gammaglobulins.
Good luck, Dr Olson