Quick Test And Clinic Characteristic Study On Legionnaire's Disease In Children

Legionella is a cytozoic gram-negative bacillus. The latest reporthas found that it has 42 strains and 64 serogroups,among whichlegionella pneumophila is closest to human diseases. Presentlylegionnaires's disease has been listed as one of 29 infectious diseaseswhich have been threatening the health and safety of mankind. And insome other countries it is included in legal communicable disease. Asits main manifestaion is pneumonia, in a narrow sense, legionnaires'sdisease is also called legionella pneumonia.Legionella has come to be recognized and paid attention to since1976 when an outbreak of infectious disease with pneumonia as itsmajor symptoms occurred among veterans attending a convention ofAmerican Legion in Philadelphia in the USA. The following year,American CDC isolated the pathogen and named it Legionella. Theydiscovered that this outbreak of legionnaires's disease was originallydue to the contamination of air conditioner system. With the outbreak ofsevere acute respiratory syndrome (SARS), a newly emerging infectiousdisease in spring in 2003, legionnaires's disease again aroused greatinterest and attention in the medical field. Clinic features oflegionnaires's disease include fever, cough, dyspnea and a sheet ofshade changes on chest X-ray. Besides, outbreak, epidemic as well asinfectivity are also significant characteristics of Legionnaires's disease.The epidemiological features and clinic manifestations of LegionellaPneumonia are terribly similar to those of SARS, so it is urgent to beexcluded while diagnosing SARS. It will benefit a lot to our country, tothe society, to the doctors and patients if we can reduce the number ofSARS suspicious cases and such detention or quarantine. The infection of legionella pneumophila usually occur in adultsand related reports are also common, while there are few studies onchildren's infection of legionella. On this occasion that SARS are stillepidemic and out of control, it become urgent and necessary for us toknow about the clinic features of children's legionella infection andestablish quick and sensitive detection techniques.Purpose: To establish a PCR assay to test legionella peumophila byanalyzing legionella peumophila mip gene; associated with serologicalTAT, to find out the clinic features of children's legionella infection.Methods1. Establishment of PCR method: Primers were designed according to legionella peumophila mip genesequence. Pneumococcus and non-legionella pneumophila Lm wereused as evaluation system for PCR detection. The tested bacteria were used as positive control, and the blanktubes were used as negative control.2. PCR assay were adopted to detect the sputum and pharynx secretionof 65 children patients with respiratory inflammation. The DNA of the clinic specimens and experimental bacteria wereextracted by classic saturated phenol-chloroform method. The primerswere designed according to the legionella pneumophila mip genesequence and then 628bp mip gene segments were amplified. The genesegments of Lp1—14 and other strains as well as clinic specimens werealso amplified. The amplification products were electrophoresed on 2%agarose gel and the results were observed under the ultraviolet light. 3. The venous blood were collected from the patients and the serumswere isolated to be tested by TAT.Results: 628bp specific segments were found in the PCR products oflegionella pneumophila type 1-14, while no such amplificationsegments were found in the PCR products of pneumococcus andnon-legionella pneumophila Lm; and the sensitivity of legionellapeumophila DNA was 2.1pg/ul. Among the 65 specimens, there were 6in whose PCR production 628bp gene segments were found, and thepositive rate was 9.23%. Among the 6 cases, 4 of them were TAT testedpositively, and the other 2 were negatively. The symptom for one of the6 patients was fever to be observed, 2 were upper respiratory trackinfection and the other 3 were pneumonia. All of their states of illnesseswere controlled by combination with macrolide antibiotics or switchingto them.Conclusion:1. The PCR method established by legionella pneumophila mip gene forthe detection of legionella pneumophila has high specificity and strongsensitivity, and it can be widely used. It is valuable to the earlydiagnosis of legionlella pneumonia.2. Legionella pneumophila exists in infectious diseases of therespiratory system in pediatrics. In this study, among the 65 patientswith respiratory system infection, 6 patients were found legionellapneumophila infection by PCR assay, and the positive rate was 9.23%,while by TAT assay, 4 patients were found legionella pneumophilainfection, and the positive rate was 6.15%. This indicates that thesensitivity of PCR assay is higher that that of TAT assay.3. Clinically legionella pneumophia usually display sever pneumonia,generalized infection with refractory pneumonia as the major symptom.Since its clinic manifestations are not so typical, the pediatrician shouldpay much attention to it so as to avoid misdiagnosis and missingdiagnosis. For all the Lp1-14, 628bp specific segments could be amplifiedusing the primers designed according to the legionella pneumophiaMip gene sequence, while for the non-legionella peumophila Lm and pneumococcus, no such segments could be found. Amongthe 59 children cases that PCR detection were negative, there were 2cases whose sputum specimens were cultured were foundAlpha-hemolytic-streptococcus and Neisser bacterium, however nospecific gene segments were found in their PCR products. It suggestedthat this pair of primers only amplified legionella pneumophia gene. Inaddition, the sensitivity of this experiment has reached the level of2.1pg/ul DNA, which sensitivity is higher than that of traditionalserological antibody detection. Since the detection of PCR method is...