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This year's popular Mycoplasma pneumoniae pneumonia (MPP) is somewhat strange.

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This year, there is a strange outbreak of Mycoplasma pneumoniae pneumonia (MPP). MPP is caused by a pathogen called Mycoplasma pneumoniae, which does not have a cell wall. It is believed that the current outbreak of MPP may be related to previous COVID-19 infections. People of all ages can be susceptible to MPP, with children over 5 years old being the most affected. MPP is an atypical infectious disease and is not currently classified as a notifiable infectious disease, but it is contagious. The main mode of transmission is through respiratory droplets, such as coughing, sneezing, and nasal secretions. It can also be transmitted through fecal-oral route and airborne aerosols. Indirect contact with contaminated clothing and towels has a low risk of transmission. The incubation period of MPP is long, usually 2-3 weeks, during which the pathogen can replicate without causing symptoms. Family members often experience sequential infections, and multiple rounds of infections can occur. Common symptoms of MPP include fever, cough (usually dry and can last for weeks to months), headache, sore throat, loss of appetite, and chest pain. Antibody tests for MPP can determine past infections but cannot distinguish recent infections. Antibodies IgM and IgG are used for diagnosis, with IgM levels peaking 7-9 days after infection and lasting for several months, while IgG levels peak about 2 weeks later and can persist for several years. There is a lack of safe drugs for children to treat MPP, as the majority of Mycoplasma pneumoniae strains have developed resistance to macrolide antibiotics. Currently, the only available drugs for children are tetracyclines and fluoroquinolones, but they have potential side effects and require careful evaluation and parental consent. There is currently no vaccine available to prevent MPP, and the protective antibodies produced after infection do not last long,

The Mycoplasma pneumoniae pneumonia (MPP) that is popular this year is somewhat strange.#

1. Pathogen Knowledge#

  • Mycoplasma pneumoniae (MP for short, characterized by the absence of a cell wall)
  • Note: There are many types of mycoplasma, and the main ones that cause diseases in humans are Mycoplasma pneumoniae, Mycoplasma genitalium, Mycoplasma hominis, and Mycoplasma genitalium.

2. Strange Epidemic#

  • Mycoplasma pneumoniae pneumonia has not been widely spread in the past.
  • The current epidemic of Mycoplasma pneumoniae pneumonia in the autumn and winter of this year may be related to previous COVID-19 infections.
  • People of all age groups are susceptible to Mycoplasma pneumoniae, with children over 5 years old and adolescents being the most susceptible.
  • Mycoplasma pneumoniae pneumonia is an atypical pathogenic infection and is currently not classified as a notifiable infectious disease, but it is contagious.
  • Some schools in Tianjin have started to collect data on students with Mycoplasma pneumoniae pneumonia
  • Mycoplasma pneumoniae infection is not uncommon, but most infected individuals have no symptoms or only mild symptoms.
  • Using methods similar to COVID-19 nucleic acid testing, the detection rate of Mycoplasma pneumoniae in respiratory secretions of children is between ≤3% and 56%.
    • Spuesens EB, Fraaij PL, Visser EG, et al. Carriage of Mycoplasma pneumoniae in the upper respiratory tract of symptomatic and asymptomatic children: an observational study. PLoS Med 2013; 10.
    • Jain S, Williams DJ, Arnold SR, et al. Community-acquired pneumonia requiring hospitalization among U.S. children. N Engl J Med 2015; 372:835.
    • Palma S C, Martínez T MA, Salinas S M, Rojas G P. [Asymptomatic pharyngeal carriage of Mycoplasma pneumoniae in Chilean children]. Rev Chilena Infectol 2005; 22:247.
    • Wood PR, Hill VL, Burks ML, et al. Mycoplasma pneumoniae in children with acute and refractory asthma. Ann Allergy Asthma Immunol 2013; 110:328.

3. Wide Transmission Routes#

  • Mainly transmitted through respiratory droplets, such as secretions during coughing, sneezing, and runny nose.
  • It can also be transmitted through fecal-oral transmission and airborne aerosol transmission.
  • It can also be indirectly transmitted through contact with clothing, towels, and other items contaminated with the pathogen, but the probability of transmission is low.

4. Long Incubation Period#

  • Generally 2-3 weeks, which is relatively long. During this period, the mycoplasma proliferates in large quantities but without symptoms.
  • In families, sequential infections often occur, for example, after the older child recovers, the younger child may develop symptoms.
  • Multiple rounds of infections can even occur, for example, after the older child recovers, the younger child recovers, and then the older child becomes infected again.

5. Common Symptoms#

  • 86%-96% of children will have a fever.
  • 85%-96% of children will have a cough, usually a dry cough that may last for weeks to months.
    • Meyer Sauteur PM, Unger WWJ, van Rossum AMC, Berger C. The Art and Science of Diagnosing Mycoplasma pneumoniae Infection. Pediatr Infect Dis J 2018; 37:1192.
    • Wang K, Gill P, Perera R, et al. Clinical symptoms and signs for the diagnosis of Mycoplasma pneumoniae in children and adolescents with community-acquired pneumonia. Cochrane Database Syst Rev 2012; 10.
  • Other symptoms may include headache, sore throat, loss of appetite, and chest pain below the sternum.
  • The fever is generally around 39℃.
  • Most coughs are dry without phlegm, but phlegm may appear when the cough worsens.

6. Is Antibody Diagnosis Useful?#

  • Hospitals conduct tests for two types of mycoplasma antibodies: IgG and IgM.
  • A single positive result for IgM and IgG cannot determine whether the infection occurred recently or in the past.
  • A single positive result for IgM and IgG can only indicate a previous infection with Mycoplasma pneumoniae, which may have already been resolved.
  • IgM antibodies begin to rise 7-9 days after infection, peak at 3-6 weeks, and persist for several months.
  • IgG antibodies start to rise and peak about 2 weeks later than IgM antibodies and persist for several years without disappearing.
    • Meyer Sauteur PM, Jacobs BC, Spuesens EB, et al. Antibody responses to Mycoplasma pneumoniae: role in pathogenesis and diagnosis of encephalitis? PLoS Pathog 2014; 10.
  • Changes in IgM levels during multiple tests over a period of time, such as a sudden increase, indicate a new infection.
  • Blood routine examination usually shows normal blood cell counts.
  • Chest X-rays and CT scans can only determine the extent of lung inflammation.

7. Lack of Safe Medications for Children#

  • Previously, macrolide antibiotics such as azithromycin, clarithromycin, and roxithromycin were the preferred drugs.
  • Due to the overuse of antibiotics, more than 90% of Mycoplasma pneumoniae in the Asian region had developed resistance to macrolide antibiotics as early as 2000.
  • Therefore, azithromycin and other macrolide antibiotics are no longer the first choice.
  • Currently, there are only two types of drugs available for emergency use: tetracyclines and fluoroquinolones.
  • Representative drugs of the new tetracycline class: doxycycline, minocycline.
    • Side effects: yellowing of teeth and enamel hypoplasia.
    • Only suitable for children over 8 years old.
  • Representative drugs of the fluoroquinolone class: levofloxacin, moxifloxacin.
    • Side effects: risk of cartilage damage and tendon rupture.
    • Use in children under 18 years old is considered off-label.
    • Use in children under 18 years old requires a comprehensive evaluation of risks and benefits and obtaining parental informed consent (i.e., willingness to take risks).
    • National Health Commission: Treatment Plan for Mycoplasma pneumoniae Pneumonia in Children (2023 Edition)
  • Current situation: There are no safe and effective antibiotics available for children under 8 years old who are infected with Mycoplasma pneumoniae and develop Mycoplasma pneumoniae pneumonia.

8. Sufficient Dosage and Treatment Course to Avoid Recurrence#

  • If azithromycin is still effective, it must be used in a standardized manner.
    • For example, oral administration should be done 1 hour before meals or 2 hours after meals.
    • For example, use a three-day or five-day treatment regimen with a 3-4 day interval, and the treatment course should be sufficient.
  • If using new tetracyclines or fluoroquinolones, the same applies: sufficient dosage and treatment course.
    • Avoid recurrence of symptoms, such as relief of symptoms followed by sudden high fever.

9. Can Vaccines be Used for Prevention?#

  • Unfortunately, there are currently no vaccines available on the market to prevent Mycoplasma pneumoniae pneumonia.
  • Moreover, the protective antibodies produced after infection have a short duration.
  • Therefore, there is a possibility of secondary or multiple infections in the short term.

10. References for Further Study#

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