Diagnostic Value of Nasopharyngeal Aspirates in Children with Lower Respiratory Tract Infections

Background： The accuracy of nasopharyngeal aspirate （NPA） specimens in detecting lower respiratory pathogens remains controversial. The objective of this study was to evaluate the diagnostic accuracy of aspirates （NPAs） specimen in lower respiratory tract infections （LRTIs） in children. Methods： The prospective study was designed to collect the data of paired NPAs and bronchoalveolar lavage fluids from children with acute LRTIs from January 2013 to December 2015. All specimens were subjected to pathogen detection： bacterial detection by culture, Mvcoplasma pneumoniae （Mp） detection by polymerase chain reaction assay and virus （influenza A and B viruses, parainfluenza virus [PIV] Types 1 and 3, respiratory syncytial virus, and adenovirus） detection by immunofluorescence assay. The diagnostic accuracy analysis of NPAs was stratified by age ≤3 years （n = 194） and 〉3 years （n = 294）. Results： We collected paired specimens from 488 children. The positive rate of pathogen was 61.6%. For Streptococcus pneumoniae, NPA culture had the specificity of 89.9% and negative predictive value of 100% in age ≤3 years, the specificity of 97.2% and negative predictive value of 98.9% in age 〉3 years. For Mp, the positive predictive values of NPA was 77.4% in children ≤3 years, and 89.1% in children 〉3 years. For PIV III, NPA specimen had the specificity of 99.8% and negative predictive value of 96.5% in children ≤3 years. For adenovirus, NPA had the specificity of 97.8% and negative predictive value of 98.4% in age ≤3 years, the specificity of 98.9% and negative predictive value of 99.3% in age 〉3 years. Conclusions： NPAs are less invasive diagnostic respiratory specimens, a negative NPA result is helpful in ＂rule out＂ lower airway infection; however, a positive result does not reliably ＂rule in＂ the presence of pathogens.

Droplet generation due to two health care procedures

Preliminary experiments are carried out to characterize the droplets generated in two aerosol-generating health care procedures,i.e.taking nasopharyngeal aspirates（NPA）and nebulizer therapy.Glass slides and water-sensitive paper（WSP）are used to collect large droplets when taking NPA.Droplet stain-marks on glass slides are counted under a microscope,and then a size analysis is performed.During nebulizer therapy dust monitors are used to detect small droplets and droplet nuclei at different positions around the nebulizer and in the room.From the preliminary results it is found that taking NPA can stimulate coughing and generate large droplets.Nebulizers can generate more than tens of millions fine droplets ranging from 0.3 to 20 μm per minute,a large volume of which can escape from the holes on the nebulizer＇s facemask and disperse in the whole room.Droplets coagulate on the inner surface of the mask and the volunteer＇s face,suggesting a great possibility of drug solution contamination by patients＇ secretion during nebulizer therapy.