Review of Respiratory Medicine - Volumen 24, Número 4 - December 2024

Original Articles

Abbreviated Pitt Bacteremia Severity Score in Bacteremic Pneumococcal Pneumonia

Índice de gravedad de bacteriemia de Pitt abreviado en neumonía bacteriémica por neumococo

ABSTRACT

Objective: To compare the abbreviated Pitt score (qPitt) with the CURB-65 and ATS (American Thoracic Society) scores to predict mortality, in a cohort of patients with bacteremic pneumococcal pneumonia.

Materials and Methods: A cross-sectional study was carried out including a cohort of patients with clinical and radiological criteria for pneumonia and with isolation of Strep­tococcus pneumoniae in blood cultures, during the period between January 2012 and May 2019. Age, sex, comorbidities and mortality during hospitalization were analyzed. CURB-65, ATS and qPitt scores were calculated, and their ROC (receiver operating characteristic) curves were compared.

Results: 153 patients were analyzed. The mean age was 54 years and the overall mortality was 34%. The ROC curves showed areas under the curve of 0.8072, 0.7654 and 0.6900 for qPitt, ATS and CURB-65 scores, respectively. The qPitt showed the highest area under the curve (AUC), with a statistically significant difference with respect to the CURB-65 (p 0.0020), a sensitivity of 73% and specificity of 85%, with a positive likelihood ratio of 4.82 for a score of 2 points or more.

Conclusion: The qPitt demonstrated high sensitivity and specificity for predicting mor­tality, and its performance is equivalent to the widely used ATS and CURB-65 scores.

Key words: Streptococcus Pneumoniae, Bacteremia, Severity score

 

RESUMEN

Objetivo: Comparar el rendimiento del índice (score) de Pitt abreviado para mortali­dad, con respecto a los índices de CURB-65 y ATS, en una cohorte de pacientes con neumonía bacteriémica por neumococo.

Materiales y Métodos: Se realizó un estudio transversal en el que se incluyó una co­horte de pacientes con criterios clínicos y radiológicos de neumonía y con aislamiento de Streptococcus pneumoniae en hemocultivos, durante el período comprendido entre enero de 2012 y mayo 2019. Se analizaron edad, sexo, comorbilidades y mortalidad durante la internación. Se calcularon los índices de CURB-65, ATS y de Pitt abreviado y se compararon sus curvas ROC (receiver operating characteristic).

Resultados: Se analizaron 153 pacientes cuya edad promedio fue de 54 años; la mor­talidad global fue del 34 %. Las curvas ROC mostraron áreas bajo la curva de 0,8072, 0,7654 y 0,6900 para los índices de qPitt, ATS y CURB-65, respectivamente. El de Pitt abreviado mostró la mayor área bajo la curva, con una diferencia estadísticamente signi­ficativa con respecto al CURB-65 (p 0,0020) y una sensibilidad del 73 % y especificidad del 85 %, con un likelihood ratio positivo de 4,82 para un puntaje de 2 o más puntos.

Conclusión: el índice de Pitt abreviado demostró tener elevada sensibilidad y especi­ficidad para predecir mortalidad, con un rendimiento equiparable a los índices de ATS y CURB-65, ampliamente utilizados.

Palabras clave: Streptococcus Pneumoniae, Bacteriemia, Score de severidad

Received: 02/07/2023

Accepted: 12/19/2024

  INTRODUCTION

 

Streptococcus pneumoniae is a gram-positive diplo­coccus comprising more than 90 serotypes, which are defined by the polysaccharide composition of their capsule.¹

Among communicable diseases, lower respirato­ry tract infections –primarily community-acquired pneumonia (CAP)– account for the highest mortal­ity rates, with pneumococcus being the primary etiological agent of these infectious syndromes. According to some studies, the pneumococcus is implicated in 25% to 68% of cases, depending on the diagnostic methods available, and co-infection with other germs is common.²

Nasopharyngeal colonization by pneumococcus is extremely common, occurring in 40% to 95% of the pediatric population and 1% to 10% of adults.³ Pneumococcus can also cause localized infections or invasive pneumococcal disease (IPD), which includes pneumonia with bacteremia, meningitis, and sepsis.⁴

IPD is associated with high morbidity and mortality rates worldwide.⁵ The World Health Organization estimates that pneumococcal infec­tions cause 1.6 million deaths annually, including 1 million in children under 5 years of age.⁶

The development of an invasive form of the disease depends on the host factors (age and under­lying conditions) and bacterial virulence (mainly the serotype).^5,7

Host factors associated with a higher risk of IPD and greater mortality include solid tumors, diabetes, cardiovascular diseases, chronic kidney disease/dialysis, liver cirrhosis, and neurological diseases. Interestingly, other conditions such as HIV, asplenia, oncohematological diseases, COPD, and autoimmune diseases are not associated with such risk.⁸

The isolation of pneumococcus in blood cultures from hospitalized patients with pneumonia varies between 5% to 20%, according to different stud­ies.^9-11 The correlation between the severity of the condition, as measured by different severity scores, and the presence of bacteremia has been a topic of debate.^12,13

Despite the availability of critical care units and multiple antibiotic regimens, the morbidity and mortality associated with CAP remain high. Approximately 20% of patients require hospital­ization, with mortality rates in this group ranging from 30% to 50%.^14,15

Early identification of patients at greater risk of having poor outcomes is vital. This requires know­ing the predisposing risk factors for developing severe forms of CAP that support the creation of more precise severity scores. Currently, the most commonly used scores for CAP are the CURB-65 and ATS scores.

The Pitt Bacteremia Score (PBS) has been used for decades as an objective measure of severity in bacteremia caused by gram-negative germs or sepsis.^16,17 Additionally, there is an abbreviated ver­sion of the PBS (qPitt) which incorporates binary variables (Table 1) that are exclusively clinical and independently associated with mortality after 14 days. Battle et al used Cox regression to define five independent variables associated with mor­tality in patients with gram-negative bacteremia. They established a score based on these variables (qPitt) and compared its performance with qSOFA. The qPitt demonstrated better performance in predicting mortality 14 days after blood cultures were obtained.¹⁸

 

 

OBJECTIVE

To compare the qPitt with the CURB-65 and ATS scores in a cohort of patients with bacteremic pneu­mococcal pneumonia with regard to their ability to predict mortality.

METHODS

A cross-sectional study was carried out including a cohort of patients with clinical and radiological criteria for pneumo­nia and with isolation of pneumococcus in blood cultures, during the period between January 2012 and May 2019.

Age, sex, comorbidities and mortality during hospitali­zation were analyzed. The CURB-65, ATS and abbreviated qPitt scores were applied to such cohort (Table 1).

The corresponding ROC curves were calculated with these scores for mortality prediction, and they were com­pared against one another. The best cutoff point for the qPitt score was determined.

RESULTS

153 patients were analyzed. The average age was 54 years, with 42% being women, and the median hospital stay was 11 days. The most common comorbidities were: smoking (39%), HIV (20%), alcoholism (20%), diabetes (17%) and oncological diseases (17%). 66% of the population (101 pa­tients) had one or more comorbidities. The overall mortality rate was 34%. The ROC curves showed values of 0.6900 for the CURB-65, 0.7654 for the ATS and 0.8072 for the qPitt (Fig. 1). The qPitt score demonstrated a sensitivity of 73% and a specificity of 85%, with a positive likelihood ra­tio (LR+) of 4.82 for a score of 2 or more points. No significant difference was found between the ROC curves of qPitt and ATS (p = 0.2293) or be­tween ATS and CURB-65 (p = 0.1559). However, there was a significant difference between qPitt and CURB-65 (p = 0.0020).

DISCUSSION

In cases of diseases with high prevalence and high morbidity and mortality, it be­comes crucial to have easily applicable and rapid severity scores, with high sensitivity and specificity, for proper use of resources. This approach allows for appropriate treat­ment and monitoring based on the probable course of the disease.¹⁹

Initially, the PBS was validated as a severity score for bacteremia caused by gram-negative germs, both community-acquired and hospital-acquired.^20,21 It has proven to be a useful and simple tool due to its lower complexity and more accessible variables compared to other scores, such as APACHE II, which is commonly used in critical care units.²²

Furthermore, it has also been validated for other bacteremic diseases, including those caused by Staphylococcus aureus²³ and pneumococcus. Yu et al found a high correlation between the PBS and APACHE II, with the PBS demonstrating even greater predictive value for mortality (81 vs. 74.9).²⁴ Feldman et al analyzed various severity scores (PBS, modified ATS, IDSA/ATS, CURB-65, and PSI) and their effectiveness in identifying patients with severe conditions who would benefit from admission to an intensive care unit. They found a better correlation between high scores on the PBS and modified ATS.²⁵

Furthermore, for the purpose of developing a simpler score, Battle S. et al identified indepen­dent, exclusively clinical predictors of mortality and created the qPitt score. This score has also been validated for bacteremia caused by gram-negative germs and Staphylococcus aureus.^18,26

In our study, we collected an extensive database over seven years of patients with pneumonia and pneumococcal bacteremia, and we have applied the severity scores that are commonly used in our setting (IDSA/ATS and CURB-65) and com­pared them with the qPitt score. The selection of patients with clinical and radiological criteria for pneumonia associated with bacteremia ensures, on the one hand, the identification of the etiological agent (excluding patients with sputum cultures, considering the high prevalence of pneumococcus in the nasopharynx of asymptomatic individuals) and, on the other hand, the diagnosis. The asso­ciation between severity and bacteremia remains somewhat unclear, with conflicting reports on this topic. Campbell et al found in a prospective multicenter study, a poor correlation between the severity of the condition as assessed by the PSI score (Pneumonia Severity Index) and the microbiological findings in blood cultures.¹² Levy et al found that among ICU-admitted patients, the microbiological yield from blood cultures was 46%, while in those who did not require intensive care, the yield was only 7.75%.²⁷ Similarly, Waterer et al also describe a higher incidence of positive blood cultures in patients with more severe conditions. However, they conclude that blood culture results do not produce significant changes in clinical outcomes, suggesting that the utility of this tool would be limited.¹³

The mortality rate in our study was 34%, which is higher than the findings from other series, for example, Kyaw et al, who collected the data from all the patients with pneumococcal bacteremia from Scotland between 1999 and 2001 and re­ported a mortality rate of 10.6% in patients over 65 years old and between 1-5% in the rest of the population.²⁸ However, Rock et al described a mortality rate of 21.2% in a 2013 study conducted in a tertiary-care center in Ireland.²⁹ Our mortal­ity rate is higher than the one mentioned in the references and in most of the studies around the world, especially those involving large regional populations, but it aligns more closely with the findings from tertiary-care centers. This variation in mortality could be attributed to several factors of the host, including inappropriate antibiotic use (no penicillin-resistant strains were found in our series), vaccination rates, and the virulence of different pneumococcus serotypes (a limitation in our study, as we did not have vaccination records or data on serotypes).

In our series, we observed that 53 patients (36.6%) had a qPitt score ≥2, and of these, 38 patients (71.7%) died. 58 patients met the ATS criteria (at least two minor criteria or one major criterion), and their mortality rate was 56.8% (n = 33). For CURB-65, 69 patients had a score of 2-3, with a mortality rate of 36% (n = 25). Finally, 15 patients had a score of 4-5, with a mortality rate of 80% (Table 2).

CONCLUSION

Severity scores are an essential tool for classify­ing patients at the onset of any disease, allowing therapeutic efforts to be tailored according to the current needs and the clinical progression of the condition. In our series, we found that the qPitt score performs similarly to the commonly used scores, although further prospective evaluation would be necessary.

Conflict of interest

The authors have no conflicts of interest to declare in relation to the topic of this publication.

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