Mycoplasma pneumonia is "coming on strong", scientific cognition and response are the key

Author: Zhu Dandan, attending physician at Xuanwu Hospital, Capital Medical University

Reviewer: Wang Changyuan, Chief Physician, Xuanwu Hospital, Capital Medical University

I believe everyone still remembers that in the winter of 2023, before the smoke of the fight against the new coronavirus pneumonia had dissipated, mycoplasma pneumonia hit hard, and the respiratory departments and pediatric outpatient and emergency departments of major hospitals were overcrowded and hard to find a bed. In fact, one of the important reasons for this run on medical resources is that the public is relatively unfamiliar with mycoplasma pneumonia, knows very little about it, and is prone to tension and even panic. Today, let's talk about mycoplasma pneumonia so that we can calmly deal with this disease and better protect our lungs.

Figure 1 Copyright image, no permission to reprint

1. Definition of Mycoplasma Pneumonia

Mycoplasma is not a newly discovered pathogen. It was discovered as early as 1898. Its size is between bacteria and viruses. It is obviously different from bacteria because it has no cell wall. There are more than 120 named mycoplasmas, of which only 4 are human pathogens, namely Mycoplasma hominis, Ureaplasma urealyticum, Mycoplasma genitalium and Mycoplasma pneumoniae. Among them, Mycoplasma pneumoniae can cause pneumonia, while Mycoplasma hominis, Ureaplasma urealyticum and Mycoplasma genitalium mainly cause urogenital tract infections. Mycoplasma pneumoniae was first isolated from the sputum of a patient with primary atypical pneumonia by Eaton et al. through tissue culture in 1944. It was called "Eaton factor" at that time. As early as the 1940s, there were reports of pneumonia caused by Mycoplasma pneumoniae abroad. Mycoplasma pneumoniae infection can cause upper respiratory tract infection and acute bronchitis, and can also affect the lower respiratory tract and cause mycoplasma pneumonia.

2. Epidemiological characteristics of mycoplasma pneumonia

Mycoplasma pneumoniae is one of the most common pathogens of community-acquired pneumonia. A global survey on the etiology of community-acquired pneumonia showed that mycoplasma pneumonia accounted for 12% of community-acquired pneumonia and more than 50% of all atypical pathogens in community-acquired pneumonia. The incidence of mycoplasma pneumonia in my country is even higher. In two national surveys on community-acquired pneumonia in adults in my country, the proportion of mycoplasma pneumonia was 20.7% and 38.9% respectively. The infection rate of mycoplasma pneumoniae has exceeded that of Streptococcus pneumoniae, becoming the most common pathogen of community-acquired pneumonia. Pulmonary inflammation caused by mycoplasma pneumoniae infection can affect the bronchi, bronchioles, alveoli and lung interstitium, is contagious, and can be transmitted through droplets and direct contact.

Mycoplasma pneumonia is sporadic throughout the year, with the incidence rate gradually increasing in the summer and reaching a peak in late autumn or winter. Mycoplasma pneumonia has an incubation period of 7 to 13 days, and can be as long as 21 days. Children are susceptible to mycoplasma pneumonia because their immune systems are not yet fully developed and their respiratory defenses are weak. However, the elderly with multiple chronic diseases and young and middle-aged people with poor immunity are also prone to mycoplasma pneumonia.

3. Clinical manifestations of mycoplasma pneumonia

The most prominent symptom of mycoplasma pneumonia is dry cough, accompanied by fever, sore throat, otitis, sinusitis, occasional chest pain, and blood in sputum. Special attention should be paid to the fact that mycoplasma pneumonia can cause a variety of extrapulmonary manifestations, such as abdominal pain, diarrhea and other gastrointestinal symptoms, high transaminase, impaired liver function, measles-like or scarlet fever-like rash, myocarditis, impaired consciousness and other symptoms of meningoencephalitis, hemolytic anemia, and arthritis. Physical examination of the lungs often shows no positive signs, and dry and wet rales can be heard in a few patients. Therefore, what needs to be reminded here is that even if the doctor does not hear lung rales during auscultation, it does not mean that the diagnosis of pneumonia can be ruled out. Whether a lung imaging examination is needed should be determined by the opinions of professional doctors.

Figure 2 Copyright image, no permission to reprint

The total white blood cell count and neutrophil ratio in the peripheral blood of patients with mycoplasma pneumonia are generally normal, but may be elevated in a few patients, and C-reactive protein is usually significantly elevated.

In addition, unlike common bacterial pneumonia which usually manifests as a single consolidation shadow or flake-like infiltration shadow in the lower lung, mycoplasma pneumonia more often affects the upper lung or both lungs at the same time. Depending on the affected area, the CT manifestations are diverse, including ground-glass shadows, "tree-bud signs", lattice shadows, dot-like, flake-like high-density exudative shadows, consolidation shadows, etc.

4. Diagnosis of Mycoplasma Pneumonia

The detection methods of Mycoplasma pneumoniae include Mycoplasma pneumoniae culture, Mycoplasma pneumoniae antigen detection, Mycoplasma pneumoniae antibody detection and molecular biological detection. Mycoplasma pneumoniae culture is the "gold standard" for diagnosing mycoplasma pneumonia, but Mycoplasma pneumoniae grows slowly, requiring 3 to 4 weeks or even longer, with low sensitivity and low clinical value, so it is not used as a routine test. Mycoplasma pneumoniae antigen detection is one of the bases for early diagnosis of infection. It has high specificity, low sensitivity, and high false negative rate. If the test is positive, it can be confirmed, but if the test is negative, the possibility of Mycoplasma pneumoniae infection cannot be ruled out. Mycoplasma pneumoniae antibody detection includes immunoglobulin M (IgM) and IgG antibodies. IgM antibodies generally appear within 1 week after infection; IgG antibodies often appear 2 weeks to 1 month after infection, and the IgG antibody titer reaches a peak in 3 to 6 weeks, which can last for several months to several years, and the early false negative rate is high. If the clinical suspicion of Mycoplasma pneumoniae infection is high, the patient should be re-examined regularly. IgM antibody positive can confirm Mycoplasma pneumoniae infection, but IgG antibody positive does not mean that Mycoplasma pneumoniae infection is currently present, because IgG antibody can also be positive if Mycoplasma pneumoniae infection has occurred in the past. Therefore, the IgG antibody titer can be dynamically monitored. If it increases dynamically by 4 times or more, Mycoplasma pneumoniae infection can be confirmed. Molecular biological testing has the advantages of high specificity and fast detection speed, and is considered to be the new "gold standard" for diagnosing Mycoplasma pneumoniae. However, due to problems such as the location and timing of specimen collection, there is also a high problem of false negatives, and positive results have diagnostic value.

Figure 3 Copyright image, no permission to reprint

5. Treatment of Mycoplasma Pneumonia

Mycoplasma pneumonia is self-limiting. Most mild patients can recover without treatment and have a good prognosis. Only some patients will develop severe pneumonia. Early use of antibiotics can alleviate symptoms and shorten the course of the disease. The general course of treatment is 10 to 14 days. Because mycoplasmas do not have cell walls, drugs that act on cell walls, such as penicillins, cephalosporins, and carbapenems, are ineffective against mycoplasma pneumonia. Macrolide drugs, such as roxithromycin and azithromycin, are the first choice for mycoplasma pneumonia in children, but the resistance rate of macrolide drugs in adults is as high as 80%. Quinolones, including levofloxacin and moxifloxacin, are the first choice for mycoplasma pneumonia in adults, but quinolones have an effect on skeletal muscle development and are not suitable for minors under 18 years old. Tetracycline drugs, including doxycycline and minocycline, may cause yellowing of teeth and poor enamel development, and should not be used in children under 8 years old. For children with mycoplasma pneumonia that is resistant to macrolides, the use of medication requires professional doctors to weigh the pros and cons and make comprehensive considerations.

Figure 4 Copyright image, no permission to reprint

References:

[1] Wunderink RG, Waterer GW. Clinical practice. Community-acquired pneumonia[J]. New England Journal of Medicine, 2014, 370(6): 543-551. DOI:10.1056/NEJMcp1214869.

[2] Zhao Shunying, Qian Suyun, Chen Zhimin, et al. Diagnosis and treatment guidelines for Mycoplasma pneumonia in children (2023 edition) [J]. Infectious Disease Information, 2023, 36(4): 291-297.

[3] Infection Group, Respiratory Diseases Branch, Chinese Medical Association. Expert consensus on the diagnosis and treatment of Mycoplasma pneumonia in adults[J]. Chinese Journal of Tuberculosis and Respiratory Diseases, 2010, 33(9): 643-645.

[4] National Health Commission of the People's Republic of China. Guidelines for the diagnosis and treatment of Mycoplasma pneumonia in children (2023 edition)[J]. International Journal of Epidemiology and Infectious Diseases, 2023, 50(2):79-85.

[5] Zou Yuhang, Li Mengyao, Zhang Yuanyuan, et al. Research progress in detection of Mycoplasma pneumoniae infection[J]. Chinese Journal of Pediatrics, 2023, 61(3): 274-277.