Recently, some friends around me have coughs and fevers. Some say it is influenza, some say it is Mycoplasma pneumoniae, and some say it is adenovirus… Rapid identification of the type of pathogen can provide an important basis for early clinical diagnosis and treatment decisions. There are so many pathogens, how to detect them? Let’s listen to the introduction from the experts from Peking University Third Hospital!
1. What are the common pathogens of respiratory infections?
①Influenza virus: It belongs to the family Orthomyxoviridae and is divided into three types: A, B, and C. Among them, type A and type B are more common. Influenza A viruses are prone to mutation and can be further divided into subtypes such as H1N1, H3N2, H5N1, and H7N9. The incubation period is short, usually 1 to 3 days.
② Respiratory syncytial virus: It belongs to the Paramyxoviridae family and has only one serotype. Infants and children are generally susceptible. The human body cannot produce permanent and specific antibodies after infection, so repeated infections may occur.
③ Parainfluenza virus: It belongs to the Paramyxoviridae family. It is a respiratory virus that causes mild flu-like symptoms. The population is generally susceptible. Infants and young children are prone to lower respiratory tract infections. The incubation period is 2 to 5 days.
④ Adenovirus: It belongs to the Adenoviridae family, and the population is generally susceptible. People of all ages can be infected with adenovirus, but infants, young children, the elderly, people with low immune function, young adults living in groups and medical staff are more susceptible. The incubation period is generally 3 to 10 days.
⑤Coxsackievirus: It is an enterovirus, divided into two types, A and B. It can infect the human body through the digestive tract and respiratory tract. Human infection with Coxsackievirus can easily cause herpetic anginitis and non-paralytic poliomyelitis. Wait for changes. The incubation period is generally 1 to 3 days.
⑥New coronavirus: It belongs to the beta coronavirus, with multiple mutant strains, and the population is generally susceptible. The incubation period of most patients with new coronavirus infection is 3 to 7 days, and the incubation period of individual patients is relatively long, which can reach 14 days.
① Streptococcus pneumoniae: It is one of the main pathogens of pneumonia and can also cause other respiratory infections and blood infections.
② Klebsiella pneumoniae: usually causes pneumonia and urinary tract infections, and some strains may become resistant to antibiotics.
③ Haemophilus influenzae: It is a common pathogen of respiratory tract infections, especially in children.
④ Legionella pneumophila: may cause severe pneumonia and is mainly spread through water sources.
Mycoplasma pneumoniae and Chlamydia pneumoniae
Mycoplasma pneumoniae and Chlamydia pneumoniae are microorganisms between bacteria and viruses. They are common pathogens causing acute respiratory tract infections in adolescents. They have a long incubation period, usually 2 to 4 weeks.
2. How to detect different types of pathogens?
Detection of pathogens is critical for early diagnosis, treatment and controlling the spread of disease. At present, pathogen detection mainly includes: antigen detection, antibody detection and nucleic acid detection.
The type of infection is confirmed by detecting pathogen-specific antigens in the sample. This method is simple and fast, and the specimen types are usually nasopharyngeal swabs and oropharyngeal swabs. It is suitable for early screening of acute infections and is convenient for self-testing at home. However, the sensitivity of antigen detection is relatively low.
Past or current infection is confirmed by testing the levels of specific antibodies produced in a person’s blood. Clinically, two types of antibodies, specific IgM and IgG, are mainly detected.
IgM is the earliest antibody to appear. It usually appears about 1 week after infection, reaches a peak around 2 to 4 weeks and then gradually decreases. The maintenance time is short. Therefore, pathogen-specific IgM detection can be used for the early diagnosis of acute infection or infectious diseases. .
IgG type antibodies appear later than IgM, but last longer, and usually indicate past infection or are used in population epidemiological surveys. Clinically, dual serum samples can be used to detect pathogen-specific IgG antibody levels based on the dynamic changes in antibody content. The first sample should be collected as early as possible at the beginning of the disease (acute phase), and the second sample should be collected 2 to 3 weeks later. (Convalescence period), if the titer of specific IgG antibodies in the second sample is more than 4 times higher than that of the first sample, it also has great diagnostic value for acute infectious diseases.
It should be reminded that antibody testing may have false negatives or false positives and should be combined with comprehensive clinical analysis.
Nucleic acid amplification testing
Infection is confirmed by analyzing the nucleic acid sequence of the pathogen. The main types of specimens for respiratory infections include nasopharyngeal swabs, oropharyngeal swabs, sputum specimens, and bronchoalveolar lavage fluid.
This method has strong specificity, high sensitivity, and high accuracy, and has good clinical value especially in early stages of infection or low viral load. However, nucleic acid testing usually requires testing equipment, personnel qualifications, and laboratory conditions. High requirements, and the detection time is relatively long.
3. What respiratory pathogen detection programs does Peking University Third Hospital have?
Three nucleic acid tests for respiratory pathogens: respiratory syncytial virus, human parainfluenza virus, and adenovirus.
Seven nucleic acid tests for respiratory pathogens: influenza A virus, influenza B virus, respiratory syncytial virus, human parainfluenza virus, adenovirus, Mycoplasma pneumoniae, and Chlamydia pneumoniae.
Respiratory virus six-plex nucleic acid detection: influenza A virus, influenza B virus, respiratory syncytial virus, human parainfluenza virus type I, human parainfluenza virus type III, adenovirus.
Respiratory virus six-plex nucleic acid detection + Mycoplasma pneumoniae DNA: influenza A virus, influenza B virus, respiratory syncytial virus, human parainfluenza virus type I, human parainfluenza virus type III, adenovirus, and mycoplasma pneumoniae.
Nucleic acid detection of respiratory pathogenic bacteria: Streptococcus pneumoniae, Staphylococcus aureus, methicillin-resistant Staphylococcus aureus, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Acinetobacter baumannii.