Abstract
We assessed the frequency and the potential role of respiratory viruses on disease outcomes in hospitalized patients and lung transplant recipients who underwent a bronchoalveolar lavage (BAL) for an acute respiratory infection. BAL specimens (148) were analyzed by reverse transcription-polymerase chain reaction for the presence of 11 different viruses, as well as Mycoplasma pneumoniae, Chlamydophila pneumoniae, and Legionella pneumophila. Respiratory viruses were identified in 34 of 117 BAL specimens (29%) obtained in patients with a suspected respiratory infection and in only 2 of 31 control subjects (7%) (p < 0.01). M. pneumoniae was identified in five additional cases. Only 30% of cases that were virus positive by molecular methods were also positive by cell culture analysis. Rhinovirus was the most frequently identified virus (56% of cases) followed by respiratory syncytial virus (27%). In lung transplant recipients, the rate of viral infections was 55% in cases with respiratory symptoms compared with only 4% in control subjects (p < 0.001). In these cases, respiratory viral infections were associated with significant lung function abnormalities. By using reverse transcription-polymerase chain reaction assays, we frequently identified respiratory viruses in BAL specimens of patients hospitalized with lower respiratory tract infections. These viruses were associated with high morbidity, particularly in lung transplant recipients.
Lower respiratory tract infections (LRTIs) are a leading cause of morbidity, hospitalization, and antibiotic use in patients with immunosuppression and/or chronic lung diseases; however, the etiology remains undetermined in 48 to 70% of cases (1–3). This lack of diagnosis exists because appropriate lower respiratory tract samples are often not available and routine diagnostic procedures are limited both in their sensitivity and in the number of agents routinely targeted. Among undiagnosed agents, respiratory viruses are thought to contribute to a substantial number of LRTIs in hospitalized patients, especially when such viruses are circulating in the community. Hence, there is a need to establish the precise impact of respiratory viruses in patients hospitalized with an LRTI. Although nucleic acid detection by reverse transcription-polymerase chain reaction (RT-PCR) has considerably improved our ability to diagnose these infections (4, 5), the use of this tool is limited by the large number of viral types and subtypes and by the difficulty to collect appropriate lower respiratory specimens. Therefore, few studies have attempted to evaluate the role of respiratory viruses by systematically using sensitive RT-PCR assays on appropriate samples such as bronchoalveolar lavage (BAL) specimens. In particular, we lack information on the potential role of viruses that are difficult to grow, such as rhinovirus, human coronavirus, and human metapneumovirus.
The detection of viral RNA in a respiratory sample suggests a viral contribution to respiratory symptomatology and pathology. This issue is of particular importance in immunocompromised patients who may be infected with several agents and who are prone to bacterial superinfections. In this study, we addressed this question by correlating clinical findings with the presence or absence of a proven viral infection.
In addition to respiratory viruses, Mycoplasma pneumoniae, Chlamydophila pneumoniae, and Legionella pneumophila also cause community outbreaks, share similar clinical features, and present diagnostic difficulties. Their impact in immunocompromised hosts likewise needs to be established in large studies.
The purpose of this study was to employ molecular methods to detect and identify 11 different respiratory viruses and three atypical agents in patients from whom a BAL and a viral culture were performed after an acute respiratory event. Our goal was to assess the incidence and the potential impact of respiratory viral infections on disease outcome in a patient population that was at high risk of complications. This knowledge should enable a more rational use of new antivirals, antibiotics, and vaccines when available. Portions of the results of this study have been previously reported in the form of an abstract (6).
We selected specimens over a 1-year period (2001–2002) to cover all four seasons, as respiratory viruses have a marked seasonal distribution that is specific for each virus type. During the study period, 678 BAL procedures were performed in our institution. In 348 procedures, viral cultures were performed, based on the decision by the physician in charge, and independent of this study. Among these 348 samples, we excluded samples obtained from the same patient that were collected less than 1 week apart, as well as the few samples that were inadequate to conduct all the assays (26 of 348 [8%]). Of the remainder, we selected every other sample, a total of 148 specimens. Although some patients had multiple BAL procedures during the study period, each sample and episode were analyzed independently. Samples were subsequently analyzed for the presence of respiratory viruses and atypical bacteria by technicians blinded to any previous microbiological results.
Based on the clinical chart review with microbiological results still blinded, patient BAL specimens were distributed into two groups according to the likelihood of a respiratory infection. Group 1 consisted of BAL samples obtained from patients with any clinical suspicion of respiratory infection. Patients included in this group had at least one of the following acute respiratory symptoms: rhinorrhea, cough, sputum, dyspnea, unexplained lung function decline, or new chest X-ray abnormalities. This group also included immunocompromised patients presenting with persistent fever. Group 2 included BAL samples from patients who underwent fiberoptic bronchoscopies for reasons other than suspicion of a respiratory infection (i.e., routine follow-up of lung transplant recipients, investigation of noninfectious interstitial lung diseases, or pulmonary nodules) and were considered as the control group. Because lung transplant recipients constituted a large and well-defined subgroup of patients enrolled in this study, we performed an additional analysis of this subgroup. According to the previously mentioned criteria, BAL specimens from lung transplant recipients were further distributed into subgroups 1 and 2.
Subjects were considered immunocompromised if at least one of the following conditions was present: hematopoietic stem cell transplantation, solid organ transplantation, hematologic malignancies, chemotherapy for cancer, autoimmune or collagen diseases, long-term use of 10 mg or more of prednisone per day, any other immunosuppressive treatment, human immunodeficiency virus infection, liver cirrhosis, or diabetes. The presence of one of the following diseases was considered an additional comorbidity: cardiovascular disease, renal insufficiency, alcoholism, chronic respiratory disease, or solid cancer.
A case report form recorded patient characteristics, underlying disease, comorbidities, immunosuppressive therapy, survival at 1 month after the infectious episode, and radiologic findings. Report forms for each episode were completed in parallel by investigators blinded to microbiological investigations. In all lung transplant recipients, the results of sequential spirometries and transbronchial biopsies performed as part of the clinical follow-up were also recorded and analyzed in both groups. The ethics committee of the University Hospitals of Geneva approved the study.
BAL procedures were performed following a standardized protocol. Accordingly, 30 to 50 ml of sterile saline solution were instilled three times into the distal bronchial tree, either at the site of the radiographic abnormality or in the middle lobes. All BAL specimens were separated into aliquots and processed similarly for subsequent analysis. Gram stain, acridine orange, auramine, and Giemsa colorations were performed for direct identification of bacteria, mycobacteria, fungi, and parasites. Cultures for bacterial identification were inoculated under standard aerobic conditions on four different media as well as on specific media for mycobacterium detection. Pulmonary bacterial infection was considered only when quantitative BAL sample results were 104 cfu/ml or more for the pathogen in association with clinical symptoms; otherwise, it was not considered an infection.
For virus detection, four different cell culture lines (human embryonic fibroblasts, A549, Medin-Darby canine kidney [MDCK], and LLC-MK2 cells) were inoculated in tubes at two different temperatures (37°C and 33°C).
Qualitative RT-PCR assays were performed on all specimens for the following 10 different respiratory viruses: influenza A and B, respiratory syncytial virus (RSV) A and respiratory syncytial virus B, parainfluenza 1 and 3, human rhinovirus, human metapneumovirus, and coronaviruses OC43 and E229. We also completed this series by determining the presence of the recently discovered human coronavirus NL63 in a subgroup of 120 specimens for which we had stored DNA remaining. Adenovirus was detected by cell culture only. These 120 cases were equally distributed across all groups and subgroups, representing 78%, 81%, 87%, and 78% of cases in Group 1, Group 2, Subgroup 1, and Subgroup 2, respectively. We also performed PCR assays for the detection of M. pneumoniae, C. pneumoniae, and L. pneumophila. After collection, approximately 5 ml of BAL specimen were immediately placed in 2 ml of viral transport media. Crude BAL mixed in the viral transport media conserved at 4°C were used to inoculate cells within 4 hours, and 2 ml were aliquoted and frozen at −80°C. The frozen aliquot was untouched and thawed only to conduct the RT-PCR/PCR assays. PCR analysis for the human coronavirus NL63 was performed during a second time period using stored cDNA.
RNA was extracted from 200 μl of each specimen by using 400 μl of lysis buffer (HCV Amplicor Specimen Preparation Kit; Roche Diagnostics Corporation, Indianapolis, IN) followed by incubation at room temperature for 10 minutes. Propanol (650 μl) was added, and the tubes were centrifuged at 5,000 × g for 15 minutes. The resulting pellet was washed with 1 ml of ethanol (70%) followed by another centrifugation at 5,000 × g for 5 minutes. The ethanol was then removed, and the pellet was dried at room temperature for 15 minutes. RNA was dissolved in 30 μl of nuclease-free water (Promega Product, Catalys AG, Wallisellen, Switzerland) and immediately processed for reverse transcription. For M. pneumoniae, C. pneumoniae, and L. pneumophila identification, 500 μl of the sample was used. Extraction was performed using a phenol–chloroform–isoamyl alcohol procedure followed by ethanol precipitation.
Reverse transcription was performed using Superscript II RNase H− Reverse Transcriptase (Invitrogen, Life Technologies, Basel, Switzerland) in a reaction mixture containing 5 μl of extracted RNA, 4 μl of 5 × First-Strand Buffer (250-mmol Tris-HCl [pH 8.3], 375-mmol KCl, 15-mmol MgCl2), 2 μl of dithiothreitol (0.1 M), 100 U Superscript II RNase H− Reverse Transcriptase, 2 μl of deoxynucleoside triphosphate (1.5 mmol; Amersham Biosciences Europe GmbH, Otelfingen, Switzerland), 20 U of RNase Inhibitor (Roche Diagnostics GmbH, Mannheim, Germany), 1.5 μl of Primer Random p(dN)6 (Roche Diagnostics GmbH, Rotkrenz, Switzerland), and 4 μl of nuclease-free water. Reverse transcription was performed for 60 minutes at 42°C followed by incubation at 95°C for 10 minutes. The tubes were placed on ice and were immediately processed for PCR.
PCR (total reaction of 25 μl per well) was performed using 5 μl cDNA, Taqman Universal Mastermix containing Rox passive reference (Applied Biosystems, PE Europe B.V., Rotkrenz, Switzerland) and appropriate concentrations of the primers and probes described in Table 1
Virus (Target Gene) | Primer Forward | Primer Reverse | Probes |
|---|---|---|---|
| Influenza A (matrix) | 5′-GGA CTG CAG CGT AGA CGC TT-3′ | 5′-CAT CCT GTT GTA TAT GAG GCC CAT-3′ | 5′-CTC AGT TAT TCT GCT GGT GCA CTT GCC A-3′ |
| Influenza B (hemagglutinin) | 5′-AAA TAC GGT GGA TTA AAT AAA AGC AA-3′ | 5′-CCA GCA ATA GCT CCG AAG AAA-3′ | 5′-CAC CCA TAT TGG GCA ATT TCC TAT GGC-3′ |
| RSV A (N gene) | 5′-CTC AAT TTC CTC ACT TCT CCA GTG T-3′ | 5′-CTT GAT TCC TCG GTG TAC CTC TGT-3′ | 5′-TCC CAT TAT GCC TAG GCC AGC AGC A-3′ |
| RSV B (N gene) | 5′-TTC CTA ACT TCT CAA GTG TGG TCC TA-3′ | 5′-CTG GTT TCT TGG CGT ACC TCT ATA C-3′ | 5′-TCC CAT TAT GCC TAG ACC TGC TGC ATT G-3′ |
| Parainfluenza 1 (hemagglutinin-neuraminidase) | 5′-CAT TAT CAA TTG GTG ATGC-3′ | 5′-CTT AAA TTC AGA TAT GTA TCC TG-3′ | 5′-CTT AAT CAC TCA AGG ATG TGC AGA TAT A-3′ |
| Parainfluenza 3 (hemagglutinin-neuraminidase) | 5′-CTC GAG GTT GTC AGG ATA TAG-3′ | 5′-CTT GGG AGT TGA ACA CAG TT-3′ | 5′-AAT AAC TGT AAA CTC AGA CTT GGT ACC TGA CTT-3′ |
| Rhinovirus (5′ noncoding region) | 5′-GCA CTT CTG TTT CCC C-3′ | 5′- GGC AGC CAC GCA GGC T-3′ | 5′-AGC CTC ATC TGC CAG GTC TA-3′ |
| 5′-AGC CTC ATC TGC CAG GTC TG-3′ | |||
| Human metapneumovirus (polymerase) | 5′-TGC TCA TGC CCA CTA TAA AAG GT-3′ | 5′-TCT GTT AAT ATC CCA CAC CAA TGA C-3′ | 5′-CCA TGG AAA TAA TTC TCT CTC TTG TTC AGG AAC T-3′ |
| Coronavirus OC43 (polymerase) | 5′-CGC CGC CTT ATT AAA GAT GTT G-3′ | 5′-GGC ATA GCA CGA TCA CAC TTA GG-3′ | 5′-AAT CCT GTA CTT ATG GGT T GGG ATT-3′ |
| Coronavirus 229E (polymerase) | 5′-TGG AGC GAG GAT CGT GTT C-3′ | 5′-TAG GCT GTG ACA GCT TTT GCA-3′ | 5′-TGT TCT CAC GCT GCT GTT GAT TCG CT-3′ |
| Coronavirus NL63 (replicase) | 5′-TGT TGT AGT AGG TGG TTG TGT AAC ATCT-3′ | 5′-AAT TTT TGT GCA CCA GTA TCA AGT TT-3′ | 5′-ATG TTT CAC CAA TTG TTA GTG AGA AAA TTT CTG TTA TGG A-3′ |
| Mycoplasma pneumoniae (Cytadhesin P1) | 5′-AAG TTA AAC CCG CAA ACG CC-3′ | 5′-GGG ACC TTG TTT TTG ACC TCG-3′ | 5′-TCA CCT TTA ACC CCT TTG GCG GGC T-3′ |
| Chlamydophila pneumoniae (Pst1) | 5′-TGG AGA TAA AAT GGC TGG ACG-3′ | 5′-TAT GGC ATA TCC GCT TCG G-3′ | 5′-CAC GGA AAT AAA GGT GTT GTT TCC AAA ATC G-3′ |
| Legionella pneumophila
(16S rDNA) | 5′-CGT AAG GGC CAT GAT GAC TTG-3′ | 5′-TTG GGT TAA GTC CCG TAA CGA-3′ | 5′-ACC ATC ACA TGC TGG CAA
CTA AGG AT-3′ |
Based on previous studies, the expected number of samples positive by cell culture for at least one respiratory virus is less than 5% (9, 10), and the expected number of positive cases by molecular amplification is estimated as between 15 and 35%. For the primary analysis, we identified the number of respiratory viral infections and/or atypical bacteria observed by molecular tests in the two different groups, as well as the 1-month survival according to the presence of respiratory viruses and/or atypical bacteria. The number of RT-PCR–positive versus culture-positive cases was also compared.
In the subset of lung transplant recipients, the FEV1 was measured at the time of the BAL procedure and again 3 months later. Values were expressed as the percentage change according to the baseline values defined as the previous best FEV1 value obtained within 3 months before the BAL episode. The presence or absence of acute rejection, as defined by the International Society of Heart and Lung Transplantation, was documented in all but two patients (one in each group) with an available lung biopsy. Only acute rejections A2 or more were considered for comparison between groups. The outcome of lung recipients was assessed by recording the occurrence of bronchiolitis obliterans or bronchiolitis obliterans syndrome after the infectious episode, according to International Society of Heart and Lung Transplantation criteria and mortality after infection.
Data are presented as absolute values, percentage values, percentage-predicted values (FEV1), mean ± SD, and median (range), as appropriate. Unpaired t tests were used to compare demographic data between groups. Chi-square tests were used to compare rates of infection, acute rejection, and bronchiolitis obliterans and/or bronchiolitis obliterans syndrome between groups. Mortality rates between groups were compared using the Kaplan-Meier log rank method. These analyses were performed using the PRISM version 3.0 for Windows (GraphPad Software, San Diego, CA). A p value of 0.05 or less was considered statistically significant.
The funding source had no role in the design, data collection, analysis, or interpretation of the study or in the decision to submit the article for publication.
During a 1-year study period, 148 BAL specimens from 111 patients were analyzed. Multiple BAL procedures (mean, 2.8; range, 2–6) were performed on 21 patients. The mean age of patients was 54 years (range, 1–83), and 83 (56%) were male. Primary clinical conditions present at the time of the BAL procedure are shown in Table 2
n (%) | |
|---|---|
| Immunosuppressive therapy* | 86 (58) |
| Transplant recipients | 75 (51) |
| HIV positive (median CD4 78/mm3, range 17–384) | 15 (13) |
| Solid cancer | 15 (13) |
| Autoimmune and collagen diseases | 16 (11) |
| Cirrhosis | 4 (3) |
| Chemotherapy during hospitalization | 13 (11) |
| At least one immunosuppressive condition* | 113 (76) |
| At least one additional comorbidity* | 147 (99) |
| Bacterial and/or fungal infection in BAL specimens | 29 (20) |
| New chest X-ray infiltrate | 79 (68) |
| Antibiotic treatment | 113 (76) |
Of the 148 BAL specimens analyzed, 117 were from Group 1 and 31 from Group 2. Respiratory viruses and/or atypical bacteria were identified in 39 of 117 BAL specimens (33%) in Group 1 compared with 2 of 31 BAL specimens (7%) in Group 2 (p < 0.01). Group 1–positive BAL specimens were distributed as follows: 34 were positive for a respiratory virus by RT-PCR and/or cell culture (by cell culture only: two adenovirus, one RSV A), and M. pneumoniae infection was identified in five additional cases. Overall, a double infection was present in six cases (two viruses in five cases and one virus and M. pneumoniae in one case). The two positive cases in Group 2 included one case of rhinovirus in a lung transplant recipient and one case of influenza in a young patient with cerebral death after a cranial trauma during the influenza season. Given the circumstances for the latter patient, we did not have a complete medical history, and the BAL was performed for screening purposes before lung donation for transplantation. Among the BAL samples positive by RT-PCR for a respiratory virus, only 30% were culture positive (p < 0.001). The distribution of the different virus types identified is detailed in Table 3
n (%) | |
|---|---|
| Positive for at least one respiratory virus and/or atypical bacteria* | 39 (33) |
| Positive for at least one respiratory virus* | 34 (29) |
| Human rhinovirus | 19 (56) |
| RSV A | 5 (15) |
| RSV B | 4 (12) |
| Adenovirus | 2 (6) |
| Influenza B | 2 (6) |
| Coronavirus 229 E | 2 (6) |
| Parainfluenza 1 | 2 (6) |
| Influenza A | 1 (3) |
| Parainfluenza 3 | 1 (3) |
| Coronavirus OC43 | 1 (3) |
| Human metapneumovirus | 0 (0) |
| Coronavirus NL63† | 0 (0) |
| Positive for at least one atypical bacteria* | 6 (5) |
| Mycoplasma pneumoniae | 6 (100) |
| Legionella pneumophila | 0 (0) |
| Chlamydophila pneumoniae | 0 (0) |
We next focused our analysis on the 57 BAL procedures performed in lung transplant recipients: 31 cases in Subgroup 1 and 26 control subjects in Subgroup 2. A new chest X-ray infiltrate was present at the time of the BAL in 13 (42%) episodes in Subgroup 1 and none in Subgroup 2. The number of episodes positive for a respiratory virus was 17 (55%) and 1 (4%) in Subgroups 1 and 2, respectively, (p < 0.001). The rate of bacterial and/or fungal infections diagnosed in BAL specimens was 16% in Subgroup 1 and 23% in Subgroup 2, a difference that was not statistically significant. The rate of cytomegalovirus infection was similar in both subgroups (Table 4)
Subgroup 1 n (%) | Subgroup 2 n (%) | ||
|---|---|---|---|
| (n = 31) | (n = 26) | p | |
| Respiratory virus | 17 (55) | 1 (4) | < 0.01 |
| Rhinovirus | 9 | 1 | na |
| RSV A or B | 4 | 0 | na |
| Influenza A or B | 2 | 0 | na |
| Parainfluenza 1 | 1 | 0 | na |
| Adenovirus | 1 | 0 | na |
| Respiratory bacterial and/or fungal infection* | 5 (16) | 6 (23) | 0.4 |
| Respiratory CMV infection* | 4 (13) | 4 (15) | 0.54 |
| Respiratory HSV infection* | 0 (0%) | 0 (0%) | — |
| Blood lymphocytes, g/L | 10.3 ± 2.0 | 12.8 ± 3.6 | 0.52 |
| FEV1 (% predicted), mean ± SD† | 66.0 ± 6.4 | 78.4 ± 5.8 | 0.16 |
| Acute rejection (⩾ A2), n (%)‡ | 2/20 (10) | 5/21 (24) | 0.32 |
| BO/BOS, n (%) ¶ | 2/20 (10) | 1/21 (4) | 0.55 |
Figure 1. Change of FEV1 in three groups of lung recipients. Percentage change of FEV1 according to baseline in three groups of lung recipients. Samples were obtained during a confirmed respiratory viral infection (Subgroup 1 virus positive; circles), during a suspected but not confirmed respiratory viral infection (Subgroup 1 virus negative; triangles), and during a routine clinical control (Subgroup 2; inverted triangles). The follow-up of the FEV1 is presented in the same Subgroups 3 months later (open symbols).
[More] [Minimize]Finally, to assess whether respiratory virus could be shed chronically and asymptomatically in lung transplant recipients, we analyzed available BAL samples before and after a positive viral episode. We identified eight positive cases that fulfilled these criteria and in which BAL, performed as a routine procedure after transplantation, was available (a median of 12 weeks before and after the initial positive BAL). All of these samples tested negative for the virus identified at the time of the positive episode.
This study analyzed the presence of respiratory viruses in BAL specimens to determine their frequency and impact on LRTIs. Data showed that in hospitalized subjects (mainly immunocompromised patients) who needed a BAL procedure for an LRTI, the incidence of respiratory viral infections was very high. Indeed, RT-PCR assays targeting 11 different respiratory viruses identified a viral infection in 30% of episodes compared with only 10% by cell culture methods. This sensitive tool better estimates the frequency of respiratory viral infections in hospitalized patients and permits the identification of the cause of a respiratory event in patients who do not respond to conventional empirical antibiotic treatment.
Although mild or subclinical illness may follow a respiratory viral infection, it is generally agreed that the presence of viral RNA in respiratory secretions denotes a recent infection because these viruses are not known to cause latent infections. In healthy subjects, the infection is generally limited to the upper respiratory tract with viral clearance occurring within a few days (11, 12). Conversely, patients with comorbidities and/or impaired immune function are at a higher risk of severe LRTI complications (9–10, 13–16). To understand better whether these respiratory viruses contributed to the symptoms that prompted the BAL procedure, we specifically analyzed lung transplant recipients (Subgroups 1 and 2) because this largest subgroup is the most prone to complications. We found a high rate of viral infections (55%) in transplant recipients who received the BAL procedure. This differs significantly with the 4% of viral infections found in the control group. After the acute episode of infection, we observed a worsening of pulmonary function that persisted for more than 3 months in a substantial number of cases. This is consistent with previous reports showing a deterioration of lung function in lung transplant recipients with respiratory viral infections (10, 17–20). To assess further the significance of this finding, we identified all positive episodes in which BAL samples were available in the months before and after the viral episode. All pre- and post-BAL specimens tested negative for the virus identified during the period of respiratory symptoms, strongly suggesting that it is unusual to detect respiratory viruses without the presence of respiratory symptoms. Other events that could produce symptoms similar to viral respiratory infections such as bacterial or cytomegalovirus infection, or acute rejection in lung transplant recipients, were only identified in a very small number of cases. Taken together, the majority of our findings strongly suggest that respiratory viral infections are frequent in lung transplant recipients, particularly during the autumn–winter season when community outbreaks occur. Viral infections played an important role in the onset of respiratory symptoms, and asymptomatic shedding was uncommon.
The most frequent virus recovered was rhinovirus. This is in agreement with the knowledge that rhinovirus is the primary cause of acute viral respiratory illnesses (21). Such a high rate of rhinoviral infection in a population of hospitalized subjects has not been reported previously, although rhinovirus is a major cause of asthma exacerbation (22, 23) and has been linked to hospital outbreaks (24). This could be explained by the fact that few studies have addressed this issue by systematically applying a sensitive RT-PCR method. Rhinovirus replication is mostly limited to the upper respiratory tract, but experimental data have shown that it also replicates in the lower respiratory tract (25), and severe rhinoviral pneumonia has been described in immunocompromised hosts (9, 26, 27). Our findings corroborate these previous reports and strongly suggest that rhinovirus is a leading cause of respiratory disease in hospitalized immunocompromised hosts (28, 29).
Similar to rhinovirus, human coronavirus is generally not identified by cell culture and is not targeted by commonly used RT-PCR panels. In this study, human coronaviruses OC43 and 229E were identified in three cases. Coronavirus has been associated with nosocomial respiratory outbreaks (30) and with acute cardiopulmonary illnesses in older patients (31). The identification of coronavirus in lower respiratory tract specimens in adults has not been reported in earlier case studies. In a recent report of hematopoietic stem cell transplantation recipients, RT-PCR assays performed in 46 BAL specimens of patients with new chest X-ray abnormalities were all negative for coronavirus (27). These differences might be explained by patient selection, assay sensitivity, and seasonal pattern (32). Whether human coronavirus can easily replicate in the lower respiratory tract of immunocompromised adults needs to be confirmed in further studies. However, the SARS outbreak together with the recent discovery of a new human coronavirus that causes bronchiolitis (33) and the evidence that some animal species suffer from pneumonia (34) illustrates the potential of these viruses. We also tested 80% of specimens for the presence of the recently discovered human coronavirus NL63 (33), but all were negative. The first reports have shown that this virus can be recovered at a relatively low frequency in upper or lower respiratory tract specimens from children and adults with respiratory symptoms (33, 35). Our observation suggests that during the study period this coronavirus was an infrequent cause of respiratory diseases in our group of patients; however, our knowledge of the epidemiology and impact of this virus is still in an early stage and deserves further investigation.
In recent years, human metapneumovirus has been shown to cause respiratory diseases similar to RSV in children (36–38). However, the morbidity of human metapneumovirus in adults and in immunocompromised patients (39), as well as its seasonal distribution (40), has not been fully evaluated. Our study addressed a population of hospitalized patients during one winter season. In these patients, human metapneumovirus was not isolated. This specific seasonal characteristic is also illustrated by a relatively low frequency of influenza infections in this study, whereas in a previous study influenza was the most frequent virus recovered from BAL specimens by cell culture (10). These variations are related to the nature of the influenza virus itself and its ability to cause annual outbreaks of different intensity. The influenza epidemic during the study period was moderate compared with previous years (data not shown). RSV, on the other hand, was the second most frequent virus and is a well-known cause of severe disease in immunocompromised hosts (12, 41, 42).
Despite the use of PCR assays for identification of atypical bacteria, only a small number of M. pneumoniae cases were identified, and no C. pneumoniae or L. pneumophila infections were identified. Thus, these bacteria were an infrequent cause of illness in our study population during the time period studied. These results could be related to epidemiologic patterns but also to the use of wide-spectrum antibiotics that target these microorganisms as empirical therapy.
In conclusion, we have shown that by using appropriate and sensitive assays, respiratory viruses are frequently recovered in BAL specimens of patients hospitalized with an LRTI. When present, these viruses are associated with high morbidity, particularly in lung transplant recipients. Rapid identification of respiratory viruses in this latter population could avoid costly procedures and unnecessary treatment. The fact that therapeutic intervention with neuraminidase inhibitors, ribavirin, or immunoglobulins might be effective in cases of influenza, RSV, or other respiratory viral infections should also be considered. New drugs such as pleconaril or protease inhibitors, active against a wide range of rhinoviral strains (43), are also in development. However, very few prospective and controlled studies have been performed in hospitalized patients, and thus, the role of antiviral therapy in this population deserves further investigation (44). Nevertheless, our observation that respiratory viruses are associated with significant clinical impact strongly suggests that the timely use of PCR-based assays, followed by appropriate antiviral treatment, may have a determinant impact on clinical care and outcome, particularly in patients at higher risk for complications.
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