Diagnostic Accuracy of Clinical Tool 'STOPS' and Serum Procalcitonin for Optimizing Antibiotic Therapy in Neonates Born at ≥ 28 Weeks of Gestation with Neonatal Sepsis
1 Neonatal Intensive Care Unit, King Hamad University Hospital, Al Muharraq, Kingdom of Bahrain.
2 Department of Pediatrics, Command Hospital (SC) and Armed Forces Medical College, Pune, India.
3 Department of Neonatology, Kerala Institute of Medical Sciences, Trivandrum, India.
Received: November 8, 2020
Accepted: February 10, 2021
Mediterr J Hematol Infect Dis 2021, 13(1): e2021019 DOI 10.4084/MJHID.2021.019
| This is an Open Access article distributed
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therapy is initiated in neonates on suspicion of sepsis. Optimizing
therapy is a felt need of clinicians as prolonged injudicious use
increases mortality and morbidity risk.
Materials and Methods
1. Clinical tool 'STOPS'.
The case definitions of definite, clinical, and no sepsis in the study used as the reference standard[15,16] were adapted for our setting and were based on a combination of clinical signs, serum CRP and blood culture (Table 2). Serum PCT estimation was not used for this purpose. Serum CRP assays were done at 48 hours and repeated at 72 hours. Quantitative determination of CRP was done on Roche/Hitachi Cobas C systems on plasma using particle enhanced immune turbidimetric assay. A cut-off of ≥ 15 mg/L was considered as a positive test. In asymptomatic neonates with sterile blood culture and negative CRP at 48 and 72 hours, antibiotic therapy was stopped. Symptomatic neonates with a positive blood culture received antibiotics for 7 days, and if asymptomatic by the 7th day with a negative CRP, antibiotics were discontinued. Lumbar puncture (LP) for cerebrospinal fluid (CSF) examination for meningitis in neonates with EONS was done only in those with a positive blood culture (definite sepsis), while in LONS, it was done in all neonates with definite or clinical sepsis.
2. Case definition (reference standards) for neonatal sepsis.
The BACTEC or BacT/Alert microbial detection system was used to detect aerobic and facultative anaerobic microorganisms from the blood. Vitek-2 automated sensitivity and identification system was used for the identification of organisms. Pediatric blood culture bottles were inoculated with approximately 1 ml of the blood sample as per study protocol. Positive blood culture reports were alerted as soon as indicated by the microbial detection system, and a final report was made available by 48 hours as positive or negative.
All mothers with risk factors for EONS received IV Cefuroxime before delivery. EONS was defined as the onset of symptoms within 72 hrs of age (< 72 hrs), while LONS was defined as the onset of symptoms after 72 hrs of age (≥ 72hrs).[14,17]
Sample size calculation and statistical methods. We estimated the prevalence of definite EONS initiated on IV antibiotics to be 0.3/1000 hospitalized neonates based on a study conducted at our unit earlier. Using the nomogram for sample size calculation proposed by Carley et al. with a required confidence interval of 0.05 and desired sensitivity and specificity of 95%, the requisite sample size was 300 neonates. The data were entered in a Microsoft excel sheet, and the results were analyzed using statistical software SPSS version  The index test variables were changed to dichotomous variables and were tested using the Chi-square test or Fischer exact test with the reference standard. All p values reported are two-tailed, and a p-value of ≤ 0.05 is considered statistically significant. The sensitivity, specificity, PPV, NPV, PLR, and NLR were calculated to find the index test's diagnostic accuracy with the reference standard. An NLR of <0.2 was considered relevant. A PLR of 5-10 was taken as moderately useful and >10 as very useful. The area under the receiver operating characteristic (ROC) curve (AUC) was calculated for diagnostic accuracy of PCT in EONS and LONS. Kappa statistics were used to find out the agreement between observations recorded by the neonatal fellows and nurses.
|Table 3. Clinical characteristics of neonates in EONS and LONS groups.
There were 50/380 (13.2%) neonates in the LONS group. Of these, 5/50 (10%) were between 28-30 weeks gestational age and 10/50 (20%) between 1000 to 1500 gram bodyweight category. The LONS group's neonates were heterogeneous, with median gestation of 37.5 weeks (IQR 32.5 – 38) and a birth weight of 2550 gm (IQR 1751 – 3105). In the LONS group, 13/50 (26%) had definite sepsis, and 7/50 (14%) had clinical sepsis. Bacterial growth on blood culture was seen in 6/50 (12%) neonates with LONS (Table 3). One neonate with definite LONS was diagnosed with meningitis on cytology and biochemistry examination of the CSF.
Diagnostic accuracy of temperature recording in the EONS group at 12 hr showed a PPV of 100% and a PLR of 9.1 (7.7 – 18). Perfusion assessment at 12 hr had a PPV of 77% and PLR of 8.25 (2.3 – 29). Skin color assessment at 6 hr had a PPV of 68% and PLR of 5.77 (2.29 – 15), while at 12 hr it had a PPV of 100% and PLR of 13.5 (9.7 – 27) (Table 4). The diagnostic accuracy of PCT in the EONS group done at 12 hr showed a PPV of 33% and an NPV of 86%. The PLR was 1.3, and the NLR was 0.45 (Table 4) (Figure 1). In the LONS group, skin color's diagnostic accuracy at 12 hr had a PPV of 100%, NPV of 61%, and PLR of 11.2 (8.6 – 19.5) (Table 5). The diagnostic accuracy of PCT in the LONS group showed a PPV of 82%, NPV of 74%, PLR of 7 (1.7-29), and NLR of 0.54 (Table 5) (Figure 2).
|Table 4. Diagnostic accuracy of STOPS and PCT in EONS.|
|Figure 1. ROC curve with AUC for Procalcitonin in early onset neonatal sepsis.|
|Table 5. Diagnostic accuracy of STOPS and PCT in LONS.|
|Figure 2. ROC curve with AUC for Procalcitonin in late onset neonatal sepsis.|
In the EONS group, combining positive 'STOPS' and PCT at 12 hr revealed 289 (87.5%) neonates, with a positive index test indicating antibiotics use. Of these, there was definite sepsis in 48, clinical sepsis in 45, and no sepsis in 196 with a low miss rate of 2 neonates. In LONS, combining 'STOPS' and PCT at 12 hr showed 23 (46%) neonates, with a positive index test where antibiotics were indicated. Of these, 13 had definite sepsis, 7 clinical sepsis, and no sepsis in 3 with no missed case (Table 6).
Kappa statistics for the STOPS variables ranged between 0.810-1.0 showing perfect agreement with p=0.000.
|Table 6. Strategies for optimizing use of antibiotics in neonatal sepsis.
Oxygenation did not perform well understandably, as a significant number of preterm neonates had respiratory distress syndrome (RDS). Serum PCT alone had a very low specificity of 35%, a sensitivity of 84%, and a PLR, which was not useful. It had an NPV of 86%, which was as good as any of the STOPS parameters (Table 4). The study shows that by combining the clinical tool 'STOPS' and PCT as a treatment strategy, i.e., treating all symptomatic neonates and performing PCT at 12 hours, a nearly 60% reduction in unnecessary antibiotics use could be achieved, and which was superior to either by using STOPS or using PCT (Table 6).
For diagnosing neonatal sepsis presence of clinical symptoms and signs are essential. Only considering lab results may be erroneous as they may be incomplete (blood culture-negative sepsis) and misleading (positive CRP or hematological indices without clinical correlate). We used the clinical parameters' STOPS', which were predefined, easy to learn, and interpret, with good inter-observer reliability. Most clinical studies evaluating sepsis have used similar clinical parameters for early sepsis diagnosis.[20-23] Ohlin et al. to evaluate the clinical signs most predictive of sepsis in neonates in the NICU, used, amongst others, altered sensorium, perfusion disturbance, abnormal skin color, and increasing oxygen requirement, which are similar to our 'STOPS' parameters. It showed a statistically significant association of perfusion disturbance and abnormal skin color in identifying neonatal sepsis, similar to our observation. Increasing oxygen requirement was not predictive, which is also similar to our observation. Prediction tools for EONS as calculators have been studied by many authors and are the subject of a systematic review. The review concluded that the neonatal EOS calculator is associated with a substantial reduction in empirical antibiotics for suspected EOS. However, there are several limitations to this approach in our setting. Firstly, all the included studies were from developed countries where the rate of EONS is lower compared to the developing countries. Secondly, it does not allow application in neonates below 34 weeks. In our study, we included neonates from 28 weeks gestation upwards. Maternal group-B streptococcus (GBS) status and GBS specific intrapartum antibiotics used for risk prediction in the calculator are not relevant in our setting. The calculator allows the inclusion of clinical findings, including parameters related to sensorium, perfusion, and oxygenation similar to our 'STOPS'.
As regards LONS, our study found no sepsis in 30/50 (60%) neonates. All 'STOPS' parameters had specificity between 90-100% and PPV of 70%, with abnormal skin color having a valuable predictive ability (Table 5). Serum PCT alone had high specificity of 93% and was found to be moderately useful based on the PLR. Combining 'STOPS' and PCT did not further improve the diagnostic ability to exclude infection with surety and stop antibiotics (Table 6).
Several studies have evaluated clinical and laboratory parameters in LONS prediction models.[21,25,26] Arayici et al. introduced base excess for early diagnosis of neonatal sepsis in preterm newborns. A retrospective study by Tollner evaluated clinical and hematological parameters to create a scoring system. The study identified skin color changes, prolonged capillary refill time, and hypotonia (indicating altered sensorium) to be most predictive in the early part and later at the illness's peak. Another study by Singh et al. evaluating clinical signs in LONS for their predictive value included lethargy, temperature disturbances, and central cyanosis. The study found hyperthermia to have a specificity of 90% for definite or probable sepsis. The PPV for the 12 reported clinical signs was between 50 and 60%, except for grunting (75%) and intercostal retractions (100%). However, the study did not look at skin color changes, which in our study had the highest PLR. A prospective case-control study describing a predictive model for LONS found clinical parameters of lethargy, poor feeding, temperature disturbance, abnormal heart rate, respiratory insufficiency, and hypoxemia to have high predictive ability. The adjusted odds ratio (OR) identified poor feeding and temperature disturbance to be the most useful. Unlike earlier studies, we have included blood glucose estimation as it is routinely monitored in sick neonates, and both hyperglycemia and hypoglycemia are encountered in neonatal sepsis.[28,29]
Our study's strength is the easy interpretation of the 'STOPS' parameter, high inter-observer agreement, and optimum testing for ruling out sepsis by hematological indices, quantitative CRP, and blood culture. We have in our study proposed treatment strategies that allow early discontinuation of antibiotics. The most optimum strategy in EONS would be to treat neonates with one abnormal 'STOPS' parameter at 6 hours and perform PCT at 12 hours in those with normal STOPS at 6 hours. In LONS, the most optimum strategy would be to treat all neonates with two or more abnormal 'STOPS' parameters at 6 hours or a positive PCT test using a cut-off of > 2 ng/ml done at 12 hours. Being a single-center experience is a limitation of this study. Also, in temperature and skin color assessment at 12 hours in neonates with EONS, the high specificity and PPV of these parameters coupled with small-sample bias may have led to the high PLR estimate.
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