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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 bacterium 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, but it is more common in children over 5 years old and teenagers. MPP is an atypical infectious disease and is not currently classified as a legally 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 transmission and airborne aerosol transmission. Contact with contaminated clothing or towels can also lead to indirect transmission, although the risk is low. MPP has a long incubation period of 2-3 weeks, during which the bacterium multiplies without causing symptoms. It is common for family members to sequentially become infected. The most 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 testing can be used for diagnosis, but a single positive result for IgM and IgG antibodies cannot determine whether the infection is recent or past. Antibodies can persist for months to years. There is a lack of safe drugs for children with MPP, as the bacterium has developed resistance to many antibiotics. Currently, the recommended drugs for children are tetracycline and fluoroquinolone, but they have potential side effects and limitations for use in children. There is currently no vaccine available to prevent MPP, and the protective antibodies produced after infection do not last long, increasing the risk of reinfection. Proper and sufficient treatment with antibiotics is important to avoid recurrence of symptoms.

The popular Mycoplasma pneumoniae pneumonia (MPP) 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 human diseases 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 ages 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. It is currently not classified as a statutory 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 ranges from ≤3% to 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 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, relatively long, during which the mycoplasma proliferates in large quantities without symptoms.
  • Sequential infections often occur among family members. For example, after the recovery of the first child, the second child may develop symptoms.
  • Multiple rounds of infections can even occur, such as the first child recovering, the second child getting infected and recovering, and then the first child getting 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 pain below the sternum.
  • The fever is generally around 39°C.
  • Most coughs are dry without phlegm, but phlegm may appear when the cough worsens.

6. Are Antibody Tests Useful for Diagnosis?#

  • Hospitals conduct tests for Mycoplasma pneumoniae antibodies, including 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 only indicates 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 misuse 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 the pros and cons 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. Adequate 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: adequate 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. Learning References#

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