Discussion
CAP is a frequent cause of admission and disease burden in children worldwide and M. pneumoniae has been shown to be an important causative agent. Macrolides are generally considered an effective first choice antibacterial treatment for this condition. With a large variation in resistance rates worldwide, it is of our interest to look at the resistance rate of our local population of children comparably to nearby regions.
According to our series of patients, the resistance rate is around 43%. This is not as high as the 75% previously published group of patients from 2010 to 2013, when Mycoplasma PCR and genotype testing for point mutations were limited to selected ill patients not responding to first line treatment. Our observed resistance rate is more representative of the pattern in our local population as the sample size has increased, and patients admitted with pneumonia were more readily tested for Mycoplasma PCR and resistant strains.
Although the observed resistance rate is more representative of the local population, there are several limitations of this study. The sample population is limited to hospitalized patients with Mycoplasma associated pneumonia, and to one regional hospital of Hong Kong. With the diagnosis of CAP, the subsequent testing for atypical pathogens such as M. pneumoniae was based on the attending doctor’s clinical decision and suspicion. Therefore collaborating with other hospitals for territory-wide and routine testing would produce more comprehensive results and further accuracy in the local resistance rates with the larger data samples. Another technical limitation in identifying resistance strains is that all our patients were tested for specific resistance genotype (A2063G) by real time PCR, the position relevant to most cases of macrolide resistance since gene sequencing would be too time consuming.
A number of prior studies have shown that it is not possible to predict the presence of M. pneumoniae resistance solely on the basis of presenting manifestations or routine laboratory investigations. Similarly, chest radiography cannot be used to predict atypical bacterial infection, limited in terms of sensitivity, specificity and inter-observer variability. It is well known that a comprehensive overview of world-wide resistance is hampered by the difficulty of cultivating M. pneumoniae strains. Previously, serology remained the only available means to confirm mycoplasma infection.
Currently, the use of molecular methods such as real-time PCR offers the possible rapid identification of M. pneumoniae strains independent of serological studies. Information on resistance can guide appropriate treatment improving the clinical outcome, preventing complications and improving the length of stay. Although informative, genotype sequencing for identifying resistance is offered in selective laboratories. Therefore , we aim to identify clinical parameters or patient characteristics to guide the decision in optimizing and using alternative antibiotic therapies.
Use of alternative antibiotics as tetracyclines and quinolones for the treatment of Mycoplasma associated pneumonia have not been favoured particularly in younger age groups of children due to their potential bone growth suppression, teeth staining and enamel hypoplasia effects during tooth development or cartilage erosion in some animal studies.
Our results have shown a clinical parameter facilitating early recognition of likely MRMP to prompt earlier change in antibiotic choice. Clinically and practically on a daily basis, the use of ‘72 hours non-defervescence’ can be used as a cut off tool to facilitate recognition of likely MRMP and to support the clinical decision for earlier change of antibiotic therapy during the course of admission. Patients with MRMP treated with doxycycline achieved rapid defervescence within 24 hours. This is valuable information to avoid development of potential complications and shorten the length of stay. This could be particularly useful in clinical decisions for younger groups of patients, balancing the risks of the disease and treatment side effects when considering the use of doxycycline.
Previous literature has mentioned that children with M. pneumoniae treated with ineffective antibiotics have similar outcomes to those observed in patients infected by susceptible strains. This may indicate that mycoplasma pneumonia itself may be a self-limiting disease. [14] This seems to indicate that there may not be a need to change current macrolide use systematically in the case of mild to moderate disease, but alternatives should be considered if for persistent symptoms , clinical deterioration or evolving complications. In our study, 4 patients with MRMP developed pleural effusion. This suggests there may a difference in the rate of developing complications in mycoplasma pneumonia, particularly if the strain is macrolide resistant, as an ineffective antibiotic treatment may lead to a prolonged clinical course.
According to our data, by 72 hours, 96% of MSMP patients achieved defervescence.