Limited value of chest radiography in predicting aetiology of lower respiratory tract infection in general practice

Acute cough in outpatients: what causes it, how long does it last, and how severe is it for different viruses and bacteria?

OBJECTIVES

To describe the symptoms, duration, severity, and microbiology of lower respiratory tract infection (LRTI) in outpatients.

METHODS

Prospective cohort study of adults in US primary or urgent care with a chief complaint of cough and symptoms consistent with LRTI. Baseline data included demographics, signs, symptoms and PCR for 46 viruses and bacteria. Severity of symptoms reported for up to 28 days follow-up via diary and text message. The Bronchitis Severity Score (BSS) assessed severity at baseline; overall severity was defined as the area under the symptom severity curve.

RESULTS

Of 718 patients with complete baseline data, 618 had valid PCR results, and 443 were followed until symptoms resolved. Of those with valid PCR, 100 (16.2%) had 1+ viruses detected, 211 (34.1%) had 1+ bacteria, and 168 (27.2%) had both. Symptoms more likely with viral or mixed infection included feverishness (36.7% to 38.4% vs 18.5%), chills or sweats (36.0% to 38.1% vs 17.9%), being generally unwell (78.2% to 81.3% vs 64.9%), and myalgias (42.7% to 48.2% vs 28.6%). Colored sputum (42.9% vs 23.2% to 29.5%) was more common with bacterial infection. Mean duration of cough was 14.7 days with viruses (95% CI 13.2-16.2), 17.3 with bacteria (95% CI 15.9-18.6), 16.9 with mixed infection (95% CI 15.2-18.6), and 18.4 with no detection (95% CI 16.1-20.8). Overall severity of cough was lower for viral infections (20.9 points, 95% CI 18.6-23.3) than for other groups (range 24.2-26.3). The most common potential bacterial pathogens were Haemophilus influenza (28.0%), Moraxella catarrhalis (16.2%), and Streptococcus pneumoniae (10.2%), while the most common viral pathogens were rhinovirus (17.3%), influenza (12.8%), SARS-CoV-2 (11.5%), and seasonal coronaviruses (8.1%).

CONCLUSION

The mean duration of cough was 16.4 days. Consistent with European studies, the type of infection or potential pathogen was not an important predictor of the duration or severity of LRTI.

Radiological, epidemiological and clinical patterns of pulmonary viral infections

Respiratory viruses are the most common causes of acute respiratory infections. However, identification of the underlying viral pathogen may not always be easy. Clinical presentations of respiratory viral infections usually overlap and may mimic those of diseases caused by bacteria. However, certain imaging morphologic patterns may suggest a particular viral pathogen as the cause of the infection. Although definitive diagnosis cannot be made on the basis of clinical or imaging features alone, the use of a combination of clinical and radiographic findings can substantially improve the accuracy of diagnosis. The purpose of this review is to present the clinical, epidemiological and radiological patterns of lower respiratory tract viral pathogens providing a comprehensive approach for their diagnosis and identification in hospitals and community outbreaks.

Highly selective and sensitive online measurement of trace exhaled HCN by acetone-assisted negative photoionization time-of-flight mass spectrometry with in-source CID

Exhaled hydrogen cyanide (HCN) has been extensively investigated as a promising biomarker of the presence of Pseudomonas aeruginosa in the airways of patients with cystic fibrosis (CF) disease. Its concentration profile for exhalation can provide useful information for medical disease diagnosis and therapeutic procedures. However, the complexity of breath gas, like high humidity, carbon dioxide (CO₂) and trace organic compounds, usually leads to quantitative error, poor selectivity and sensitivity for HCN with some of existing analytical techniques. In this work, acetone-assisted negative photoionization (AANP) based on a vacuum ultraviolet (VUV) lamp with a time-of- flight mass spectrometer (AANP-TOFMS) was firstly proposed for online measurement of trace HCN in human breath. In-source collision-induced dissociation (CID) was adopted for sensitivity improvement and the signal response of the characteristic ion CN^- (m/z 26) was improved by about 24-fold. For accurate and reliable analysis of the exhaled HCN, matrix influences in the human breath including humidity and CO₂ were investigated, respectively. A Nafion tube was used for online dehumidification of breath samples. Matrix-adapted calibration in the concentration range of 0.5-50 ppbv with satisfactory dynamic linearity and repeatability was obtained. The limit of quantitation (LOQ) for HCN at 0.5 ppbv was achieved in the presence of 100% relative humidity and 4% CO₂. Finally, the method was successfully applied for online determination of human mouth- and nose-exhaled HCN, and the nose-exhaled HCN were proved to be reliable for assessing systemic HCN levels for individuals. The results are encouraging and highlight the potential of AANP-TOFMS with in-source CID as a selective, accurate, sensitive and noninvasive technique for determination of the exhaled HCN for CF clinical diagnosis and HCN poisoning assessment.

A host gene expression approach for identifying triggers of asthma exacerbations

Rationale

Asthma exacerbations often occur due to infectious triggers, but determining whether infection is present and whether it is bacterial or viral remains clinically challenging. A diagnostic strategy that clarifies these uncertainties could enable personalized asthma treatment and mitigate antibiotic overuse.

Objectives

To explore the performance of validated peripheral blood gene expression signatures in discriminating bacterial, viral, and noninfectious triggers in subjects with asthma exacerbations.

Methods

Subjects with suspected asthma exacerbations of various etiologies were retrospectively selected for peripheral blood gene expression analysis from a pool of subjects previously enrolled in emergency departments with acute respiratory illness. RT-PCR quantified 87 gene targets, selected from microarray-based studies, followed by logistic regression modeling to define bacterial, viral, or noninfectious class. The model-predicted class was compared to clinical adjudication and procalcitonin.

Results

Of 46 subjects enrolled, 7 were clinically adjudicated as bacterial, 18 as viral, and 21 as noninfectious. Model prediction was congruent with clinical adjudication in 15/18 viral and 13/21 noninfectious cases, but only 1/7 bacterial cases. None of the adjudicated bacterial cases had confirmatory microbiology; the precise etiology in this group was uncertain. Procalcitonin classified only one subject in the cohort as bacterial. 47.8% of subjects received antibiotics.

Conclusions

Our model classified asthma exacerbations by the underlying bacterial, viral, and noninfectious host response. Compared to clinical adjudication, the majority of discordances occurred in the bacterial group, due to either imperfect adjudication or model misclassification. Bacterial infection was identified infrequently by all classification schemes, but nearly half of subjects were prescribed antibiotics. A gene expression-based approach may offer useful diagnostic information in this population and guide appropriate antibiotic use.

Protective Capacity of Statins during Pneumonia Is Dependent on Etiological Agent and Obesity

Acute respiratory infections are a leading cause of death worldwide. Clinical data is conflicted regarding whether statins improve outcomes for pneumonia. Potential confounding factors including specific etiology of pneumonia as well as obesity could potentially mask protective benefit. Obesity is a risk factor for high cholesterol, the main target for statin therapy. We demonstrate that statin intervention conferred no protective benefit in the context of wild-type mice regardless of infectious agent. Statin intervention conferred either a protective benefit, during influenza infection, or detrimental effect, in the case of pneumococcal infection, in obese animals. These data suggest etiology of pneumonia in the context of obesity could be dramatically altered by the protective effects of statin therapy during bacterial and viral pneumonia.

Detection of Staphylococcus aureus in cystic fibrosis patients using breath VOC profiles

Staphylococcus aureus (S. aureus) is a common bacterium infecting children with cystic fibrosis (CF). Since current detection methods are difficult to perform in children, there is need for an alternative. This proof of concept study investigates whether breath profiles can discriminate between S. aureus infected and non-infected CF patients based on volatile organic compounds (VOCs). We collected exhaled breath of CF patients with and without S. aureus airways infections in which VOCs were identified using gas chromatography-mass spectrometry. We classified these VOC profiles with sparse partial least squares discriminant analysis. Multivariate breath VOC profiles discriminated infected from non-infected CF patients with high sensitivity (100%) and specificity (80%). We identified the nine compounds most important for this discrimination. We successfully detected S. aureus infection in CF patients, using breath VOC profiles. Nine highlighted compounds can be used as a focus point in further biomarker identification research. The results show considerable potential for non-invasive diagnosis of airway infections.

Prevalence of Atypical Pathogens in Patients With Cough and Community-Acquired Pneumonia: A Meta-Analysis

PURPOSE

Community-acquired pneumonia (CAP), acute cough, bronchitis, and lower respiratory tract infections (LRTI) are often caused by infections with viruses or Streptococcus pneumoniae. The prevalence of atypical pathogens Mycoplasma pneumoniae, Chlamydophila pneumoniae, Legionella pneumophila, and Bordetella pertussis among patients with these illnesses in the ambulatory setting has not been previously summarized. We set out to derive prevalence information from the existing literature.

METHODS

We performed a systematic review of MEDLINE for prospective, consecutive-series studies reporting the prevalence of M pneumoniae, C pneumoniae, L pneumophila and/or B pertussis in outpatients with cough, acute bronchitis, LRTI, or CAP. Articles were independently reviewed by 2 authors for inclusion and abstraction of data; discrepancies were resolved by consensus discussion. A meta-analysis was performed on each pathogen to calculate the pooled prevalence estimates using a random effects model of raw proportions.

RESULTS

Fifty studies met our inclusion criteria. While calculated heterogeneity was high, most studies reported prevalence for each pathogen within a fairly narrow range. In patients with CAP, the overall prevalences of M pneumoniae and C pneumoniae were 10.1% (95% CI, 7.1%-13.1%) and 3.5% (95% CI, 2.2%-4.9%), respectively. Consistent with previous reports, M pneumoniae prevalence peaked in roughly 6-year intervals. Overall prevalence of L pneumophila was 2.7% (95% CI, 2.0%-3.4%), but the organism was rare in children, with only 1 case in 1,765. In patients with prolonged cough in primary care, the prevalence of B pertussis was 12.4% (95% CI, 4.9%-19.8%), although it was higher in studies that included only children (17.6%; 95% CI, 3.4%-31.8%).

CONCLUSIONS

Atypical bacterial pathogens are relatively common causes of lower respiratory diseases, including cough, bronchitis, and CAP. Where surveillance data were available, we found higher prevalences in studies where all patients are tested for these pathogens. It is likely that these conditions are underreported, underdiagnosed, and undertreated in current clinical practice.

The indication area of a diagnostic test. Part II--the impact of test dependence, physician's decision strategy, and patient's utility

OBJECTIVES

Any diagnostic test has an indication area of prior probabilities wherein the gain in diagnostic certainty outweighs its loss. Here, we investigate whether indication area and the maximum diagnostic gain are robust measures if we assume test dependence, alternative physician's heuristics, and varying patient's utilities.

STUDY DESIGN AND SETTING

Three mathematical functions for the dependence of test sensitivity (Se) and specificity (Sp) on the prior disease probability were studied. In addition, three different decision heuristics for further management were explored for the case that "no test" would be done. Finally, the valuation of test outcomes was varied. A sensitivity analysis was performed to determine the impact of the alternative assumptions on the indication area and maximum diagnostic gain.

RESULTS

By assuming test dependence, the indication area shifts to higher priors and increases the maximum diagnostic gain. Decision strategies assuming a "threshold before treat" can inadvertently widen the indication area and increase the maximum diagnostic gain. Varying patient utilities will usually reduce the net diagnostic gain. A sensitivity analysis revealed the robustness of the model.

CONCLUSION

The indication area and the maximum diagnostic gain are robust measures of test performance and are easier to interpret than the classical performance measures.

Suspected community-acquired pneumonia in an ambulatory setting (CAPA): a French prospective observational cohort study in general practice

Background:

Few studies have addressed the pragmatic management of ambulatory patients with suspected community-acquired pneumonia (CAP) using a precise description of the disease with or without chest X-ray (X-ray) evidence.

Aims:

To describe the characteristics, clinical findings, additional investigations and disease progression in patients with suspected CAP managed by French General Practitioners (GPs).

Methods:

The patients included were older than 18 years, with signs or symptoms suggestive of CAP associated with recent-onset unilateral crackles on auscultation or a new opacity on X-ray. They were followed for up to 6 weeks. Descriptive analyses of all patients and according to their management with X-rays were carried out.

Results:

From September 2011 to July 2012, 886 patients have been consulted by 267 GPs. Among them, 278 (31%) were older than 65 years and 337 (38%) were at increased risk for invasive pneumococcal disease. At presentation, the three most common symptoms, cough (94%), fever (93%), and weakness or myalgia (81%), were all observed in 70% of patients. Unilateral crackles were observed in 77% of patients. Among patients with positive radiography (64%), 36% had no unilateral crackles. A null CRB-65 score was obtained in 62% of patients. Most patients (94%) initially received antibiotics and experienced uncomplicated disease progression regardless of their management with X-rays. Finally, 7% of patients were hospitalised and 0.3% died.

Conclusions:

Most patients consulting GPs for suspected CAP had the three following most common symptoms: cough, fever, and weakness or myalgia. More than a third of them were at increased risk for invasive pneumococcal disease. With or without X-rays, most patients received antibiotics and experienced uncomplicated disease progression.

Imaging of Chest Infections in Children

■ Imaging studies have limited value in the differentiation between viral and bacterial lower respiratory tract infections (moderate evidence).

■ CT provides more information than plain radiographs for complicated pulmonary infections with empyema, pleural effusion, or bronchopleural fistula (moderate evidence).

■ In immunocompromised patients, CT has been shown to characterize the type of infection better than plain radiographs (moderate evidence).

■ Ultrasound has an advantage over CT in the identification and characterization of complicated effusions (moderate evidence).

■ Early detection and therefore intervention for pleural complications of pneumonia are critical and can result in better outcomes (moderate evidence).

■ Early surgery (VATS) is more cost-effective than thoracotomy (without or with image guidance) in the treatment of empyemas in children (strong evidence).