Exploring high-risk factors for the prediction of severe mycoplasma pneumonia in children

Introduction

Mycoplasma pneumonia (MPP) remains one of the most common causes of community-acquired pneumonia (CAP) in children, accounting for 10% to 40% of hospitalized children with CAP (1-3). Due to the fact that children or young adults barely show related symptoms and seek medical care, the prevalence of MP in these individuals has been largely underestimated (4). Severe mycoplasma pneumonia (SMPP) cases in children may be accompanied with pleural effusion, pulmonary atelectasis, pneumothorax, and even necrotizing pneumonia, as well as multiple systemic complications. Even worse situation is that a small proportion of critically ill children may develop respiratory failure or even die (3). In this regard, effective identification of the risk factors of SMPP and early intervention can help improve the prognosis and decrease the incidence among children. However, the precise diagnosis turns to be difficult or even controversial, because of the non-specific clinical and radiological characteristics as well as the lack of precise diagnostic methods. In this study, we investigated the risk factors of SMPP by comprehensively evaluating the blood parameters, inflammatory response markers, blood biochemistry and other laboratory indicators using receiver operating characteristic (ROC) analysis and multifunctional logistic regression analysis. The combined results are expected to provide a basis for the early identification and prevention of SMPP. We present this article in accordance with the TRIPOD reporting checklist (available at https://tp.amegroups.com/article/view/10.21037/tp-24-293/rc).

Methods

Patients

Clinical data of 447 hospitalized children diagnosed with MPP in the Department of Pediatrics of the Sixth People’s Hospital Affiliated to the School of Medicine of Shanghai Jiaotong University, during the period from June 2020 to May 2023, were enrolled for retrospective analysis. The study was conducted in accordance with the Declaration of Helsinki (as revised in 2013). The study was approved by Ethics Committee of Shanghai Sixth People’s Hospital [No. 2023-046-(1)] and informed consent was taken from all the patients’ parents. Inclusion criteria followed the relevant diagnostic criteria of the Expert Consensus on Diagnosis and Treatment of Childhood Mycoplasma pneumoniae (2015 version) (3). Exclusion criteria included: (I) children with medical history of cardiovascular, respiratory, neurological and hematologic underlying diseases; (II) children with allergic diseases, autoimmune diseases and immunodeficiency diseases; (III) children who had recently used hormones or immunosuppressants; (IV) children with incomplete clinical data.

Methodology and data collection

Clinical data comprised general information (gender, age) and results of the first test on the day of admission of relevant laboratory tests. The laboratory items are listed as follows: (I) blood routine examination: white blood cell (WBC) count, neutrophil percentage, lymphocyte percentage, neutrophil/lymphocyte ratio (NLR), hemoglobin (Hb), red blood cell distribution width (RDW), platelet (PLT) count, platelet distribution width (PDW), and mean platelet volume (MPV), and inflammation reaction markers: C-reactive protein (CRP), interleukin-6 (IL-6), procalcitonin (PCT), serum amyloid A (SAA), erythrocyte sedimentation rate (ESR). (II) Blood biochemistry test: albumin (ALB), prealbumin (PAB), lactate dehydrogenase (LDH), triglyceride (TG), and creatine kinase isoenzyme (CK-MB). (III) Other pathogenetic tests: cytomegalovirus, Epstein-Barr virus (EBV), coxsackievirus, herpes simplex virus, influenza A/B virus, etc. The blood routine indexes were detected by SYSMEX XN-9000 automatic hematology analyzer, CRP was detected by Promen-200, IL-6 and PCT were detected by Roche Cobas e602 automatic chemiluminescence analyzer, and SAA was detected by EXPEN65 specific protein analyzer. The related indexes of blood biochemistry test were detected by Hitachi Labospect 008AS blood biochemistry analyzer. All of the above laboratory tests were performed by our laboratory staff.

MPP was documented as follows: single MP antibody (doxycycline) titer ≥1:160 or a >4-fold change in 2 serum MP antibody titers combined with MP nucleic acid testing. With reference to the diagnostic criteria related to severe pneumonia in the Diagnostic and Treatment Criteria for Community-Acquired Pneumonia in Children (2019 edition) (5), all the hospitalized children were divided into the ordinary MPP group and the SMPP group, according to the severity of the disease and changes. Specifically, SMPP was defined if one of the following manifestations was at presence: (I) poor general condition; (II) markedly increased respiration: respiratory rate (RR) >70 beats/min in infants, RR >50 beats/min in older children; (III) impaired consciousness; (IV) intermittent apnea and respiratory distress (groaning, flaring of nostrils, and triple concavity sign); (V) extent of pulmonary infiltration with multilobar involvement or ≥2/3 of the lungs involvement; (VI) pleural effusion, pneumothorax, pulmonary atelectasis, lung necrosis, lung abscess; (VII) pulse oximetry ≤0.92; (VIII) accompanied by extrapulmonary complications.

The criteria for the determination of combination of multiple pathogens were as follows: positive antibodies to 2 or more pathogens (influenza A/B virus, cytomegalovirus, EBV, coxsackievirus, herpes simplex virus, etc.), and positive or positive cultures for the pathogens or positive tests for the DNA/RNA of the pathogens in the blood, sputum or throat swab or positive serological IgM, were defined as positive for multiple pathogens, and vice versa for the other pathogens.

Statistical analysis

SPSS25.0 software was applied for statistical analysis. Measurement information conforming to normal distribution was expressed as mean ± standard deviation, and t-test of two independent samples was conducted for the comparison between groups; abnormally distributed measurement information was expressed as median (P25, P75), and rank sum test was used for the comparison between groups. Count data were expressed as the number of cases or the percentage, and comparisons between groups were carried out using the χ² test. The predictive ability of the indicators with statistically significant differences was analyzed by plotting the ROC curve. Multifactor logistic regression was used to analyze each risk factor. Differences were considered significant when P<0.05.

Results

A total of 447 cases were included in this study with age ranging from 0.5 to 14 years (average age: 6.01±2.72 years), among which 260 (58.17%) children were diagnosed with normal MP and the other 187 (41.83%) ones were diagnosed with SMPP.

Comparison of the general conditions of children in the two groups

As shown in Table 1, the gender of the involved children in the two groups shows no significant difference (P>0.05). Although the average age of SMPP children was higher than that of the ordinary MPP group, the difference turned out to be not significant (P>0.05). That is to say, neither gender nor average age of the involved children would exert impact on the test results.

Comparison of peripheral blood routine related indexes between the two groups of children

Compared with that of the ordinary MPP group (Table 2), the peripheral blood neutrophil percentage and NLR of the children in SMPP group were higher, while the lymphocyte percentage was lower, and both of the differences were significant (P<0.05). A comparison of WBC count, Hb, RDW, PLT count, PDW, and MPV between the two groups of children showed that the difference was not significant (P>0.05).

Comparison of inflammation-related indexes between the two groups of children

As shown in Table 3, CRP, IL-6 and ESR of SMPP children were higher than those of the ordinary MPP group, and the differences were all significant (P<0.05), while the differences of PCT and SAA in the two groups were not significant (P>0.05). ALB and PAB of children with SMPP were lower than those of the ordinary MPP group, while LDH was higher than that of the MPP group, and the differences were significant (P<0.05). Comparatively, the differences of TG and CK-MB between the two groups were not significant (P>0.05).

ROC curve analysis of risk factors for the prediction of SMPP occurrence

ROC curve analysis of the variables with statistically significant differences in one-way comparisons was carried out to predict the occurrence of SMPP (Table 4 and Figure 1). The results showed that the cut-off values of ESR, LDH, IL-6, CRP, percentage of neutrophils, and NLR for the prediction of the occurrence of SMPP in children were 35.50 mm/h, 360.50 U/L, 20.28 pg/mL, 9.74 mg/L, 62.65%, and 2.05, respectively; while the area under the curve (AUC) was 0.639, 0.617, 0.657, 0.647, 0.618, and 0.625 (P<0.05), respectively. The combined effects of ESR, LDH, IL-6, CRP, percentage of neutrophils, and NLR on the prediction of SMPP was higher, with an AUC value of 0.732 (P<0.05).

Figure 1 ROC curves of ESR, LDH, neutrophil (N) percentage, IL-6, and combined multiple pathogens for the prediction of SMPP occurrence. ESR, erythrocyte sedimentation rate; LDH, lactate dehydrogenase; IL-6, interleukin-6; CRP, C-reactive protein; N, neutrophils; NLR, neutrophil/lymphocyte ratio; ROC, receiver operating characteristic.

Risk factor analysis for the occurrence of SMPP

As indicated by ROC curve analysis, ESR, LDH, IL-6, CRP, neutrophil percentage and NLR were predictive of the occurrence of SMPP in children, they were therefore included in the multifactorial logistic regression analysis. A value of 1 was assigned if these factors were higher than 35.50 mm/h, 360.50 U/L, 20.28 pg/mL, 9.74 mg/L, 62.65%, 2.05, respectively; otherwise a value of 0 was assigned. Combining multiple pathogens with clinical SMPP, therefore, combining multiple pathogens was also included, and combining multiple pathogens was assigned a value of 1, otherwise a value of 0. As shown in Table 5, ESR >35.50 mm/h, LDH >360.50 U/L, IL-6 >20.28 pg/mL, and CRP >9.74 mg/L were independent risk factors for the occurrence of SMPP in children (P<0.05).

Discussion

MPP is a prokaryotic cell-type microorganism without a cell wall. The pathogenic mechanism of MP infection is quite complex, coming with potential damage to the respiratory epithelium caused by the pathogen itself and the involvement of multiple aspects of immune factors of the organism, including intrinsic and adaptive immunity, which leads to clinical manifestations in the respiratory system and other systems (6-8). Recent reports have indicated increasingly higher number of SMPP cases, a high proportion of which is characterized by complications. Among these cases, a small proportion of children are unfortunately falling into critical illness and develop rapidly, which can even lead to death. Along with the in-depth research on the pathogenesis of MPP, extensive tests are being applied to the diagnosis of SMPP.

Blood parameters are traditional non-specific inflammatory markers, among which NLR, RDW, PDW and MPV are considered to closely correlate with MPP. Specifically, changes in RDW are correlated with elevated inflammatory markers, which, to some extent, can be correlated with immuno-inflammatory diseases, severe pneumonia in respiratory diseases, etc. RDW level has been recently reported to be correlated with the severity of MPP (9). MP infection can cause changes in PLT count, PDW and other indicators, while the elevated levels of platelet parameters PLT count and platelet pressure volume can be used to determine the changes in the disease of MPP; it has also been found that MP infection can lead to thrombocytopenia (10). In this work, although the Hb and PLT count levels of children in the SMPP group were lower than those in the ordinary MPP group, and the levels of RDW, PDW and MPV were higher. The differences of these factors were found statistically not significant (P>0.05) and therefore can be barely related to the severity of the MPP disease. MP infection can cause damage to the epithelial lining of the airway mucosa, impair clearance of mucus cilia, and tolerate bacterial and other pathogens. It is important to note that SMPP children are situated in a high-stress state and may have elevated levels of leukocytes and neutrophils, which serve as key cellular components of the human host defense system against infections; and the NLR reflects the systemic inflammatory state and immune response of the organism (11). In this work, we found that the peripheral blood WBC level of children in the SMPP group was higher than that of the ordinary MPP group, but the difference was not significant (P>0.05). However, the neutrophil percentage and NLR level were higher than that of the ordinary MPP group, and the lymphocyte percentage level was lower than that of the MPP group. Both of the differences were significant (P<0.05). This suggests that peripheral blood neutrophil percentage, lymphocyte percentage and NLR level can reflect the inflammatory state and severity of the disease in children with MPP, which can also be correlated with the occurrence of SMPP, keeping good consistency with the national reports (11-13).

Inflammatory response markers correlate pediatric severe mycoplasma pneumoniae pneumonia, and the commonly used ones in clinic are IL-6, CRP, PCT, SAA, ESR, etc. It is well acknowledged that IL-6 can promote the secretion of protective antibodies and enhance the production of other inflammatory factors to aggravate inflammatory injury, which has also been found to be efficient in promoting the synthesis of CRP, of which its serum level is positively correlated with the severity of the disease (8). It is documented that the level of IL-6 in bronchoalveolar lavage fluid (BALF) of the SMPP children is significantly higher than that of the ordinary MPP children (14,15). CRP is an acute phase protein synthesized by hepatocytes under the influence of IL-6 and IL-1, which can well reflect the infection status. Typically, CRP is significantly elevated in patients with SMPP, and it is correlated with the degree of lung tissue damage (16-18). ESR is also an important and effective marker of inflammatory infection and disease activity, which increases with disease activity to a more pronounced degree than CRP, and can monitor the degree of inflammatory response in children with SMPP (19). Clinically, a markedly elevated ESR level can be an early warning of the occurrence of SMPP (8). In this work, we found that the levels of CRP, IL-6 and ESR were higher in the SMPP group than in the ordinary MPP group, and the differences were all significant (P<0.05), suggesting that there was a stronger inflammatory response in SMPP children and the levels of CRP, IL-6, and ESR were related to the occurrence of SMPP. PCT is a calcitonin precursor substance with no hormonal activity, and it is highly specific for infections; while SAA is an acute-phase response protein produced by hepatocytes and then secreted into the serum, both of which are inflammatory markers of early infection. Studies have indicated that both PCT and SAA are significantly elevated in children with SMPP, reflecting the severity of the MPP condition (20-23). In this work, we did not find any differences in the levels of PCT and SAA between the two groups (P>0.05), due in large part to the differences in the changes of PCT and SAA levels in different types of infectious diseases, as well as the fact that the cases combined with other pathogens were not excluded from this work (8,24-26).

LDH is an enzyme that catalyzes the oxidation of pyruvate to lactate, and is present in the cytoplasm of almost all cells. Serum levels of LDH reflect the degree of cell membrane damage and can be used to monitor cell and tissue injury. LDH was found to be elevated in SMPP and refractory mycoplasma pneumonia (RMPP) (8,18). ALB and PAB are both acute negative time-phase reactive proteins. Relative to that of ALB, the average lifespan of PAB is shorter, which can more accurately reflect the inflammatory state and nutritional status of the body, and therefore, can be correlated with the severity of SMPP (14). In this work, the levels of ALB and PAB in the SMPP group were lower than those in the ordinary MPP group (P<0.05), which was considered to be related to the impaired synthesis of PAB in hepatocytes and overconsumption of PAB in critically ill children due to insufficient intake, accelerated metabolism, and abnormalities in the internal environment (9,27). The levels of LDH in children with SMPP were higher than those in the ordinary MPP group (P<0.05), which suggests that there is more serious lung tissue inflammation and injury in children with SMPP.

Children with SMPP are often co-infected with other pathogens. As stated before, two or more pathogens (cytomegalovirus, EBV, coxsackievirus, herpes simplex virus, influenza A/B virus, etc.) with positive antibodies or positive culture of the pathogen or positive DNA/RNA test of the pathogen, were defined as multiple pathogen positivity in this work. The results showed that the incidence of combined multiple pathogens in the SMPP group was higher than that in the ordinary MPP group (P<0.05), suggesting that the combination of multiple pathogens was associated with the occurrence of SMPP.

It was also found that ESR, LDH, IL-6, CRP, neutrophil percentage, and NLR were significantly elevated in children in the SMPP group. ROC curve analysis showed that their cut-off values for the prediction of SMPP occurrence in children were 35.50 mm/h, 360.50 U/L, 20.28 pg/mL, 9.74 mg/L, 62.25%, and 2.05, with AUCs of 0.639, 0.617, 0.657, 0.647, 0.618, and 0.625, respectively, which are in close proximity to those of national studies (13,18), suggesting that ESR, LDH, IL-6, CRP, percentage of neutrophils, and NLR can be used as an early predictor of the occurrence of SMPP, but the sensitivity of LDH, IL-6 and neutrophil percentage was not high. The AUC combining ESR, LDH, IL-6, CRP, neutrophil percentage, and NLR for the prediction of SMPP occurrence in children was determined to be 0.732, accompanied with a sensitivity of 51.30% and a specificity of 82.20%, suggesting a higher combined predictive efficacy. Further multifactorial logistic regression analysis showed that ESR >35.50 mm/h, LDH >360.50 U/L, IL-6 >20.28 pg/mL, and CRP >9.74 mg/L were the independent high-risk factors for the occurrence of SMPP in children (P<0.05). It is noteworthy that the children with these high-risk factors should be paid close attention to in the clinical treatment to prevent further deterioration.

Despite of the progress on the evaluation of high-risk factors which can potentially predict SMPP development in children, it is noteworthy that the current work falls into a single-center retrospective study, coming with limited sample size and age span, which may attenuate the sensitivity of some of the factors, such as LDH, IL-6 and neutrophil. In this regard, multicenter and large-sample studies are needed in the future. On the other hand, different infectious diseases can cause differences in the changes of some other factors, such as PCT and SAA levels. Such complicated variation can lead to the difficulty in evaluating potentially significant difference of these factors between the ordinary MPP and SMPP groups, which is expected to be further explored in near future by excluding the cases combined with other accompanied pathogens.

Conclusions

In summary, ESR, LDH, IL-6, CRP, neutrophil percentage, and NLR are significant in the early prediction of SMPP development in children, and the combined prediction efficacy is even higher. Specifically, ESR >35.50 mm/h, LDH >360.50 U/L, IL-6 >20.28 pg/mL, and CRP >9.74 mg/L are independent high-risk factors for SMPP development in children. Exploring the risk factors and early predictors of SMPP in children can help to evaluate the disease, actively intervene and improve the prognosis.

Acknowledgments

Funding: None.

Footnote

Reporting Checklist: The authors have completed the TRIPOD reporting checklist. Available at https://tp.amegroups.com/article/view/10.21037/tp-24-293/rc

Data Sharing Statement: Available at https://tp.amegroups.com/article/view/10.21037/tp-24-293/dss

Peer Review File: Available at https://tp.amegroups.com/article/view/10.21037/tp-24-293/prf

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://tp.amegroups.com/article/view/10.21037/tp-24-293/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki (as revised in 2013). The study was approved by Ethics Committee of Shanghai Sixth People’s Hospital [No. 2023-046-(1)] and informed consent was taken from all the patients’ parents.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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