Background
SCAP is the main cause of death of children under 5 years old [
1,
2]. Rapid identification of pathogens and targeted treatments could help to save lives. BALFs collected by flexible bronchoscope are ideal samples for identifing pulmonary etiology, but few cases expericed such an invasive procedure [
3‐
5]. Prior to obtaining the etiological results from BALFs, clinical empiric anti-infection treatments usually rely on the findings from other samples, including NPAs collected from upper respiratory tracts [
6‐
8]. Whether the detection results of upper respiratory tract samples could not reflect the pathogens in the lungs, caused the clinicians fail to prescribe appropriate antibiotics and led to the diseases progress was unknown. The comparison of pathogens detected between NPAs and BALs has not been adequately explored or studied [
9,
10]. In this study, we retrospectively analyzed the etiology reports of NPAs before bronchoscopy and BALFs from the same cases with SACP admitted to our hospital from January 2018 to March 2019.
Discussion
By comparing the results of etiological detection from upper respiratory tract samples (NPAs) and BALFs, this study evaluated the reliability of upper respiratory tract samples used for diagnosis of lung pathogens in pediatric SCAPs, which would be attractiv to clinicians. In clinical setting, many pediatric cases developed to severe pneumonia even after receiving empiric anti-infective therapies [
13‐
15].
Respiratory viruses are frequently detected in community-acquired pneumonia (CAP) among children of all ages globally [
16‐
18]. The majority of pathogens associated with hospitalized SCAP in children were viruses in this study, which were consistent with the finding in this field over the past decade in high disease burden low and middle income countries (LMICs) as well as in Europe and the USA [
11,
16,
19‐
23]. In this study, seven common respiratory viruses were found in 32.3% (66/204) of the BALFs tested by DFA, and such results were consistent with what we had seen over the past decade [
12]. RSV and ADV were the two most frequently detected viruses from NPAs and BALFs.
Compared to BLAFs, only about half rate of respiratory viruses were detected in NPAs, and almost all the viruses detected in NPAs were also detected in BALFs. Using virus detection in BALFs as the “golden standard”, the positive predictive value (PPV) of viruses detection in NPAs was up to 96.9% (32/33), and the negative predictive value (NPV) was 80.1% (137/171). The results suggested that half of the seven viruses detected in NPAs by DFA could be missed, but the viruses that be found might be those presented in the lungs of SCAP cases.
HI was the most frequently isolated bacterium both in NPAs and BALFs, with positive rates of 7.3% (15/204) and 5.8% (12/ 204), respectively. Other common detected bacteria including SP, SA, PA and MC were also found [
3,
6,
9,
13]. Such results were consistent with similar reports from Xiamen and other parts of the country [
24,
25]. Both HI and SP were frequently detected, which indicates the importance of the promotion of vaccines in local younger children [
26,
27]. We do not have the vaccine coverage data of HI type b (Hib) and SP because they are not included in China’s national immunization program. In a recent published paper, the researchers estimated annual national, regional, and provincial childhood mortality and morbidity attributable to Hib in 2010–2017 [
28]. Although there was not significant difference in the positive rate of bacterial culture between NPAs and BALFs, we found that the inconsistency between the two kind of samples was obviously. Possible reasons for that discrepancy include: 1)Prior to the collection of BALFs, use of antibiotics possibly led to negative HI detection in BALFs. 2)HI had different meanings in the upper and lower respiratory tracts in those patients, or caused inflammation in different parts of the airway in the same case [
29,
30]. As the length of the hospital stay increased, patient community-acquired Gram positive flora are increasingly replaced by hospital-acquired Gram negative flora, and the risk of hospital acquired pneumonia increases. This is why we chose to compare NPAs and BALFs collected within 3 days of each other. And we should mentioned that the lower bacterial potential pathogen detection in BALFs relative to NPAs might be partially contributed by nasopharyngeal colonisation with a wider range of flora than would be associated with invasive disease. Most invasive disease would be associated with SP, HI and SA, defining a lesser range of bacteria than colonised in the upper airway. Further, the types of infiltrative disease in the lower airway might also have influenced the type of bacterial pathogens detected. In a multi-site study using percutaneous lung aspirate (not BAL), SP predominated with lobar consolidation, whilst SA predominated in pleural effusion [
10]. Not knowing the types of infiltrates appreciated on imaging scans, it is difficult to know how this might has affected the results of the present study.
Respiratory viruses and bacteria were co-detected in 3.9% (8/204) of the NPAs and 6.3% (13/204) of the BALFs, respectively. Based on our previous studies, the presence of co-pathogens or co-infections might have been significantly under-estimated, but that was not the point of this study [
5,
18]. Our study proved that the detention results of NPAs were reliable in helping to identify the causes of lower respiratory tract infections when DFA was used to detect respiratory viruses in those cases. When routine bacterial culture was used for isolating the possible pathogens, inconsistent results might be presented while using NPAs and BALFs.
Our study has some limitations. Frist, in this single-center observational study, we selected SCAP pediatric patients who experienced bronchoscopy operations. The results of this study could not representthe cases with mild CAP or nosocomial pneumonia. Second, we did not use more sensitive molecular biological diagnostic methods, which might lead to low detention rates of pathogens [
18,
31,
32]. Third, the human rhinovirus (HRV) was not studied which has become identified as a more prominent lower airway pathogen than previously suspected [
5,
7,
9,
16,
17,
19,
21,
28,
30]. We still believed that our study had unique significances, given that the DFA method was based on the existent of viruses antigens judged by naked eyes with fluorescence microscope, and the routine bacterial culture, which are the two classical methods for pathogens detection. In addition, NPAs and BALFs in this study were not collected at the same time, which might lead to bias.
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