Atypical pneumonias

Community-acquired pneumonia: a correlative study between chest radiographic and HRCT findings

PURPOSE

To elucidate what kinds of lesions tend to be overlooked or misinterpreted and why they were overlooked or misinterpreted on chest radiographs in the diagnosis of community-acquired pneumonia (CAP) by comparing radiographic findings with HRCT findings.

MATERIALS AND METHODS

In 129 patients with CAP (107 bacterial and 22 atypical) and 105 healthy subjects, the chest radiographic findings were correlated with the HRCT findings. The diagnostic accuracy of each chest radiographic finding was evaluated by comparing it with the HRCT finding.

RESULTS

The false negative rate of radiographic interpretation tended to be higher for nodules and thickening of the bronchial wall, especially in patients with atypical pneumonia. The most frequent reason for false negative interpretations of nodules and bronchial wall thickening was the overlapping of these findings with airspace consolidation or ground-glass opacity (GGO). Thin lesions were the most frequent reasons for the false negative interpretation of airspace consolidation and GGO.

CONCLUSION

The chest radiographic interpretations of GGO and airspace consolidation were influenced by the thickness of lesions, and those of nodules and thickening of bronchial walls were influenced by coexisting GGO and airspace consolidation and may contribute to a misinterpretation of these lesions and an incorrect diagnosis of CAP.

The atypical pneumonias: clinical diagnosis and importance

The most common atypical pneumonias are caused by three zoonotic pathogens, Chlamydia psittaci (psittacosis), Francisella tularensis (tularemia), and Coxiella burnetii (Q fever), and three nonzoonotic pathogens, Chlamydia pneumoniae, Mycoplasma pneumoniae, and Legionella. These atypical agents, unlike the typical pathogens, often cause extrapulmonary manifestations. Atypical CAPs are systemic infectious diseases with a pulmonary component and may be differentiated clinically from typical CAPs by the pattern of extrapulmonary organ involvement which is characteristic for each atypical CAP. Zoonotic pneumonias may be eliminated from diagnostic consideration with a negative contact history. The commonest clinical problem is to differentiate legionnaire's disease from typical CAP as well as from C. pneumoniae or M. pneumonia infection. Legionella is the most important atypical pathogen in terms of severity. It may be clinically differentiated from typical CAP and other atypical pathogens by the use of a weighted point system of syndromic diagnosis based on the characteristic pattern of extrapulmonary features. Because legionnaire's disease often presents as severe CAP, a presumptive diagnosis of Legionella should prompt specific testing and empirical anti-Legionella therapy such as the Winthrop-University Hospital Infectious Disease Division's weighted point score system. Most atypical pathogens are difficult or dangerous to isolate and a definitive laboratory diagnosis is usually based on indirect, i.e., direct flourescent antibody (DFA), indirect flourescent antibody (IFA). Atypical CAP is virtually always monomicrobial; increased IFA IgG tests indicate past exposure and not concurrent infection. Anti-Legionella antibiotics include macrolides, doxycycline, rifampin, quinolones, and telithromycin. The drugs with the highest level of anti-Legionella activity are quinolones and telithromycin. Therapy is usually continued for 2 weeks if potent anti-Legionella drugs are used. In adults, M. pneumoniae and C. pneumoniae may exacerbate or cause asthma. The importance of the atypical pneumonias is not related to their frequency (approximately 15% of CAPs), but to difficulties in their diagnosis, and their nonresponsiveness to beta-lactam therapy. Because of the potential role of C. pneumoniae in coronary artery disease and multiple sclerosis (MS), and the role of M. pneumoniae and C. pneumoniae in causing or exacerbating asthma, atypical CAPs also have public health importance.

Mycoplasma pneumoniae pneumonia: CT features in 16 patients

The objective of this study was to assess the computed tomography (CT) features of Mycoplasma pneumoniae pneumonia. We retrospectively reviewed CT findings of 16 patients (M:F = 9:7, age range 1-74 years, median 9 years) with serologically proven Mycoplasma pneumoniae pneumonia and with chest CT scan available. Two distinctive patterns of CT features of M. pneumoniae pneumonia were noted between the paediatric (age < 18 years) and the adult (age > or = 18 years) groups. The pediatric group (n=11) showed lobar or segmental consolidation (100%) with frequent pleural effusion (82%) and regional lymphadenopathy (82%) and mild volume decrease of the involved lobe (73%), while four of the five adult patients showed diffuse and/or multifocal, centrilobular or peribronchovascular areas of ground-glass attenuation (80%) with a lobular distribution, and frequent thickening of interlobular septa (60%) and the bronchial walls (40%) were also detected at high-resolution CT. The CT finding of a lobar or segmental consolidation with a parapneumonic effusion seen in our children with M. pneumoniae pneumonia was similar to that of bacterial lobar pneumonia. In contrast, the CT findings noted in our adult patients consisted of a mixture of a bacterial bronchopneumonia pattern and a viral interstitial pneumonia pattern.

Acute parenchymal lung disease in immunocompetent patients: diagnostic accuracy of high-resolution CT

OBJECTIVE

The purpose of this study was to determine whether acute parenchymal lung diseases can be differentiated on the basis of the pattern and distribution of abnormalities revealed on high-resolution CT.

MATERIALS AND METHODS

High-resolution CT scans of 90 patients with acute parenchymal lung diseases (19 with bacterial pneumonia, 13 with mycoplasmal pneumonia, 21 with acute interstitial pneumonia, 18 with hypersensitivity pneumonitis, 10 with acute eosinophilic pneumonia, and nine with pulmonary hemorrhage) were independently assessed by two observers who had no knowledge of clinical or pathologic data. The observers recorded abnormalities, their first-choice diagnosis, and their degree of confidence in their first-choice diagnosis.

RESULTS

The two observers made a correct first-choice diagnosis in an average of 55 (61%) of 90 cases. Correct first-choice diagnosis was made in 50% of cases of bacterial pneumonia, 62% of mycoplasmal pneumonia, 90% of acute interstitial pneumonia, 72% of hypersensitivity pneumonitis, 30% of acute eosinophilic pneumonia, and 28% of pulmonary hemorrhage. CT findings allowed distinction between infectious and noninfectious causes in 81 (90%) of 90 cases.

CONCLUSION

High-resolution CT is helpful in the differential diagnosis of infectious from noninfectious acute parenchymal lung disease. However, high-resolution CT is of limited value in making a specific diagnosis.

Seroepidemiology of Mycoplasma pneumoniae infections in Iceland 1987-96

Mycoplasma pneumoniae is a common cause of respiratory tract infections in humans. The aim of the present study was to analyse the seroepidemiology of M. pneumoniae infections in Iceland during a 10-y period. A retrospective analysis of all serological diagnosis of M. pneumoniae infections at the Department of Medical Virology, National University Hospital in Reykjavík was performed. A total of 13,201 test results from 1987 to 1996 were reviewed and altogether 762 patients were found to have raised M. pneumoniae antibody titres, using a conventional complement fixation assay. Infections were most common amongst young people (< or=16 y) but a second peak in incidence was observed around the age of 35 y. Significant annual (p < 0.0001) and seasonal variations (p=0.0003) were observed; M. pneumoniae infections were most common during the winter period. Three major outbreaks with intervals of three to five years were observed during the observation period. Patients diagnosed during these outbreaks had higher M. pneumoniae titres than those found when infections were less frequent (p=0.0017). Furthermore, the middle aged and elderly patients (> 50 y) had significantly lower M. pneumoniae titres than younger patients (p=0.0014). The findings of this study show that M. pneumoniae infections have definite annual and seasonal variations and also confirm previous studies showing community outbreaks of M. pneumoniae infections every 3-5 y.

High resolution CT findings in community-acquired pneumonia

PURPOSE

Our goal was to clarify the high resolution CT (HRCT) findings of community-acquired pneumonia based on pathologic findings and to make a differential diagnosis between bacterial and atypical pneumonias.

METHOD

This study evaluated 32 cases with community-acquired pneumonia, including 18 cases with bacterial pneumonia and 14 cases with atypical pneumonia [mycoplasma pneumonia (n = 12), chlamydia pneumonia (n = 1), and influenza viral pneumonia (n = 1)]. HRCT images in these cases were space consolidation, ground-glass attenuation, thickening of the bronchovascular bundle, and distribution of abnormal attenuation.

RESULTS

Bacterial pneumonia frequently showed air space consolidation with segmental distribution (72.2%) that tended to locate at the middle and outer zones of the lung. Atypical pneumonia frequently showed centrilobular shadow (64.3%), acinar shadow (71.4%), air space consolidation and ground-glass attenuation with lobular distribution (57.1 and 85.7%, respectively), and tendency of the lesions to distribute at the inner layer of the lung in addition to the middle and outer layers (85.7%).

CONCLUSION

Characteristic HRCT findings of both bacterial and atypical pneumonia were demonstrated. These HRCT features seemed to reflect pathologic findings and the manner of lesional progression. This information may support the appropriate antibiotic therapy in medical practice.

[Acute respiratory insufficiency secondary to Coxiella burnetii pneumonia: a rare complication]

Acute respiratory failure secondary to Coxiella burnetii infection is an extremely rare but serious complication that usually has a good prognosis after appropriate treatment. We describe a female patient who developed acute respiratory failure secondary to Coxiella burnetii pneumonia requiring mechanical ventilation and antibiotic therapy.

In vitro susceptibilities of spotted fever group rickettsiae and Coxiella burnetti to clarithromycin

The in vitro bacteriostatic activity of clarithromycin, a new macrolide derivative, against Rickettsia rickettsii, Rickettsia conorii, and "Rickettsia israeli" was determined by the plaque assay and the dye uptake assay. Both bacteriostatic and bactericidal activities of clarithromycin against the Nine Mile, Q212, Priscilla, and ME9 strains of Coxiella burnetti were evaluated by using three cell culture systems. Clarithromycin showed improved antibacterial activity compared with that of erythromycin. A bacteriostatic activity was obtained at concentrations below the reported maximum concentration of clarithromycin in human serum (about 4 micrograms/ml) for all tested rickettsiae. MICs ranged from 1 to 2 micrograms/ml for the three Rickettsia species and from 1 to 4 micrograms/ml for the C. burnetti strains. No bactericidal activity against C. burnetti was obtained when clarithromycin was used at 4 micrograms/ml.

Atypical pneumonias. Clinical and extrapulmonary features of Chlamydia, Mycoplasma, and Legionella infections

Pneumonias caused by atypical organisms usually have extra-pulmonary features. Chlamydial pneumonia often starts with hoarseness and fever, and respiratory tract symptoms may not appear for days. Mycoplasmal pneumonia may manifest with ear pain and a nonproductive cough. Legionnaires' disease presents with high fevers and central nervous system and gastrointestinal abnormalities. Diagnosis of chlamydial infection is accomplished with serologic testing. Patients are unresponsive to erythromycin treatment and should be started on empirical doxycycline (Doryx, Vibramycin) therapy. The presence of cold agglutinins in the appropriate clinical setting permits a presumptive diagnosis of mycoplasmal infection. Clinical diagnosis of Legionella pneumonia may be made in patients with pneumonia who also have relative bradycardia with elevated serum transaminases or hypophosphatemia with gastrointestinal or central nervous system symptoms. Erythromycin is the mainstay of treatment of legionnaires' disease, but treatment failures have been reported. Doxycycline is less expensive, has a better safety profile, and is better tolerated than erythromycin.

Cerebellar disturbance in psittacosis

A previously fit man developed psittacosis with marked cerebellar symptoms and signs. He was febrile but not confused, and he responded rapidly to treatment with erythromycin. Even if respiratory symptoms are minimal, psittacosis and other atypical pneumonias should be considered in any patient presenting with fever and cerebellar involvement.

Comparison of Gen-Probe commercial kit and culture technique for the diagnosis of Mycoplasma pneumoniae infection

The Gen-Probe rapid diagnostic system was compared with a culture method for the detection of Mycoplasma pneumoniae in clinical specimens. Of 116 clinical specimens, 103 (88.8%) yielded identical results. The relative sensitivity and specificity of the probe were both 89%. Rapid turnaround time and its sensitivity and specificity indicate that the probe test is a practical method for the rapid diagnosis of M. pneumoniae infections.

Subacute thyroiditis associated with Chlamydia psittaci infection

A patient presenting with subacute thyroiditis who had evidence of chlamydial infection is reported.

Acute respiratory insufficiency from psittacosis

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Household outbreak of Q-fever pneumonia related to a parturient cat

An outbreak of febrile respiratory disease occurred over 11 days among thirteen adults in Nova Scotia, all members of an extended family and their friends. Signs of illness included bradycardia at the same time as fever, palatal petechiae, and rapidly enlarging bilateral pulmonary infiltrates. Ten of the patients had a four-fold rise in antibody to phase-2 Q-fever antigen as determined by complement fixation on acute and 4-week-convalescent serum samples. Six children of the extended family for whom a four-fold titre rise was shown had slight or no disease. Investigations showed that the illness related to having entered the home of four of the patients on 1 of 2 consecutive days. On the first day the family cat, subsequently found to have antibody to Q fever, gave birth to kittens which she nursed in a basket kept inside the entry way. Q fever has been associated with parturient cattle, sheep, and goats but family pets, particularly cats, have not previously been implicated in human illness.

Computed tomographic brain scan findings in Q fever encephalitis

Neurological involvement in Q Fever is unusual. We present a case of encephalitis due to Coxiella Burnetii with neuroradiologic findings on CT not described previously, consisting in areas of decreased absorption coefficient in the subcortical white matter of both hemispheres, predominantly in the right. Differential diagnosis must be established from viral encephalitis, of similar clinical presentation, which may show similar CT lesions to those in this case.

Overwhelming pneumonia

A classification of normal-abnormal hosts and pathogens forms the basis for discussion of the diagnosis and management of pneumonia in the critical care setting. In order to arrive at the appropriate therapy for the unusual as well as the usual causative organisms of pneumonia, individual assessment of the need for invasive procedures must be made. The critical feature, however, is to consider the wide spectrum of possibilities for each individual patient.