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Effect of sputum induction by hypertonic saline on specimen quality
Diagnostic Microbiology and Infectious Disease 39 (2001) 211–214
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Effect of sputum induction by hypertonic saline on specimen quality Christian Chuarda,b,*, Dominique Fracheboudb, Claude Regameya a Department of Medicine, Hoˆpital Cantonal, Fribourg, Switzerland Clinical Microbiology Laboratory, Hoˆpital Cantonal, Fribourg, Switzerland
b
Received 30 October 2000; accepted 15 March 2001
Abstract Microbiologic work-up of expectorated material is routinely used to search for the etiology of pulmonary infections, but sputum is often contaminated by saliva. Inhalation of hypertonic saline induces bronchial secretions and theoretically may improve specimen quality. We compared in a laboratory-blinded, randomized study the quality of sputum obtained either with induction by saline or without induction in patients with respiratory tract infection and a history of productive cough. The quality of sputum was considered good if the polymorphonuclear neutrophils (PMNs)/squamous epithelial cells (SECs) ratio was ⱖ2 or the Q (quality) score was ⱖ⫹1 on Gram stain. Forty-nine and 50 patients were able to expectorate in the induced and spontaneous sputum groups, respectively. PMNs/SECs ratio was ⱖ2 in 65% and 74% of the patients in the induced and spontaneous sputum groups (p ⫽ 0.47); for the Q score, a value ⱖ⫹1 was found in 55% and 66% of the patients of each group (p ⫽ 0.37). In conclusion, sputum induction by hypertonic saline inhalation does not improve specimen quality as judged by the PMNs/SECs ratio on Gram stain. © 2001 Elsevier Science Inc. All rights reserved.
1. Introduction Gram staining and culture of sputum is the straightest, least demanding way to search for the etiology of lower respiratory tract infections. Although these methods have been criticized for their lack of sensitivity and specificity (Altai, 1993; Chuard et al., 1999), they remain the standard microbiology exams in the field of pulmonary medicine. Unfortunately, bronchial secretions often are contaminated by saliva containing oro-pharyngeal flora. This contamination can be quantified on Gram-stained sputum by counting the number of polymorphonuclear leukocytes (PMNs) and squamous epithelial cells (SEQs) (Morin et al., 1992; Murray & Washington, 1975; Van Scoy, 1977), hence allowing to assess the quality of the specimen and to decide if further processing is relevant. In cases where bronchial or alveolar exudate production is scarce, the relative importance of contamination of sputum by saliva is greater. Inhalation of hypertonic saline irritates the airways and induces bronchial secretions; the hypertonicity of the saline also draws water into the bronchial lumen from the interstitial fluid by osmo-
* Corresponding author. Tel.: ⫹41-26-426-74-82; fax: ⫹41-26-42672-44. E-mail address: [email protected] (C. Chuard).
sis (Miller et al., 1990a). Theoretically, sputum induction is a potential means of improving specimen quality. Sputum induction has been extensively studied for the diagnosis of Pneumocystis carinii pneumonia with divergent results. While some authors reported a sensitivity of 77% to 98% compared with bronchoalveolar lavage (Leigh et al., 1989; Ng et al., 1989; Zaman et al., 1988), others could only obtain sensitivity results between 13% and 27% (Chouaid et al., 1993; Miller et al., 1990b; Miller et al., 1991). A study comparing induced sputum and spontaneous sputum found no difference between the procedures (Metersky, Alsenzadeh & Stelmach, 1998). Sputum induction is also fraught with controversy for the diagnosis of pulmonary tuberculosis (Beck & Nanda, 1962; Jones, 1966; Shata et al., 1996; Yue & Cohen, 1967). Two studies directly comparing induced and spontaneous sputum (Fishman et al., 1994; Merrick et al., 1997) reported similar yields with both methods. Surprisingly, although most sputum microbiology requests concern routine bacteriology, and not search for P. carinii or mycobacteria, we are aware of only two publications addressing the issue of the utility of sputum induction when looking for aerobic and facultative anaerobic bacteria. In a first study, Fishman and colleagues (Fishman et al., 1994) found no advantage to use induction as a routine procedure by comparing patients for the number of PMNs
0732-8893/01/$ – see front matter © 2001 Elsevier Science Inc. All rights reserved. PII: S 0 7 3 2 - 8 8 9 3 ( 0 1 ) 0 0 2 3 1 - 0
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C. Chuard et al. / Diagnostic Microbiology and Infectious Disease 39 (2001) 211–214
on Gram stain and for bacteriology culture results. On the contrary, the procedure was found useful in a very recent study by Bandyopadhyay and colleagues (Bandyopadhyay, Gerardi & Metersky, 2000) who investigated the role of induction in patients who were not able to produce sputum spontaneously. Because the literature on the utility of sputum induction for bacteriology work-up is so scarce and because this procedure is time-consuming and inconvenient for patients, we thought it would be worthwhile to address the issue in a new, comparative, blinded study. We prospectively compared the quality of sputum sent to the microbiology laboratory for Gram staining and bacterial culture when it was collected either with or without induction by hypertonic saline. Quality was assessed by evaluating the ratio between PMNs and SECs on Gram-stained specimens.
2. Materials and methods During the 1996 –1997 and 1997–1998 winters, patients hospitalized in the Department of Medicine of the Hoˆpital Cantonal, Fribourg, Switzerland, who were diagnosed with a lower respiratory tract infection, who had a history of productive cough and for whom the attending physician requested bacteriology work-up were eligible for the study. The Hoˆpital Cantonal de Fribourg is a 400-bed community hospital. When bacteriology work-up is requested, the microbiology laboratory performs a Gram stain, a culture for aerobic and facultative anaerobic bacteria and antimicrobial susceptibility testing. One hundred and twenty patients were randomized in two group: in the first group (n ⫽ 58), sputum was to be collected after induction by inhalation of 3% saline from an ultrasonic nebulizer for 10 –15 min (induced sputum); in the second group (n ⫽ 62), sputum was to be collected without induction (spontaneous sputum). The specimens were obtained by nurses who were not given special training; they had written instructions requesting that they teach patients and help them if necessary. No mouth rinse was performed before sputum collection and no chest percussion was used. If several sputum specimens were collected for a patient, only the first one was included in the study. Sputum was collected in sterile containers, stored at 4°C, transported to the microbiology laboratory within 20 h (Penn & Silberman, 1984) and processed by experienced technologists who were unaware of the mode of collection (laboratory-blinded design). The most purulent part of the sputum was Gram-stained and the number of PMNs and SEQs was recorded. The quality of the sputum was judged on the relative numbers of PMNs and SECs per field (low power magnification[10x]), using 2 methods: the simple ratio (PMNs/SECs) and the Q (quality) score. The Q score (Table 1), rated on a 7-point scale (-3 to ⫹3), is a more subtle way to evaluate the PMNs to SECs ratio and was chosen because it is proposed in a major clinical microbi-
Table 1 Calculating the Q score The Q score is calculated by adding the Q value obtained for polymorphonuclear neutrophils (PMNs) to the Q value obtained for squamous epithelial cells (SECs) PMNs per microscope fielda
Q value
0 1–9 10–24 ⱖ25
0 ⫹1 ⫹2 ⫹3
SECs per microscope fielda
Q value
0 1–9 10–24 ⱖ25
0 ⫺1 ⫺2 ⫺3
a
Low power magnification [10⫻] Adapted with permission from Morin et al. 1992
ology procedure manual (3). The quality of the sputum was considered good if the PMNs/SECs ratio was ⱖ2 or the Q score was ⱖ⫹1. Differences in proportions were analyzed using the 2 test, with Yates’ correction when appropriate. Analysis of variance (ANOVA) was used for comparing means. All tests were two-tailed. The p values less than 0.05 were regarded as significant.
3. Results During the study period, 120 patients were randomized: 58 in the induced sputum group and 62 in the spontaneous sputum group. It was possible to collect sputum from 49 patients (84.5%) in the induced sputum group and 50 patients (80.6%) in the spontaneous sputum group. In the induced sputum group, 24 patients (49%) were males, with a mean age ( ⫾ SD) of 68.5 ( ⫾ 17.1) years; 22 had pneumonia, 22 had bronchitis and 5 suffered from bronchiectasis or cystic fibrosis. In the spontaneous sputum group, 27 patients (54%) were males, with a mean age ( ⫾ SD) of 67.3 ( ⫾ 17.8) years; 29 had pneumonia, 18 had bronchitis and 3 suffered from bronchiectasis or cystic fibrosis. There were no statistically significant differences between groups for demographic characteristics or sputum production. A PMNs/SECs ratio ⱖ2 (good quality sputum) was found in 32 patients (65%) in the induced sputum group and in 37 patients (74%) in the spontaneous sputum group. This difference was not statistically significant (p ⫽ 0.47) (Table 2). A Q score ⱖ⫹1 was noted in 27 (55%) patients in the induced sputum group and in 33 patients (66%) in the spontaneous sputum group. The mean ( ⫾ SD) Q score was ⫹0.47 ( ⫾ 1.39) in the induced sputum group and ⫹0.78 (⫾ 1.34) in the spontaneous sputum group. These
C. Chuard et al. / Diagnostic Microbiology and Infectious Disease 39 (2001) 211–214 Table 2 Sputum quality with and without saline induction Patient group
PMNs/SECs ⱖ2 Q score ⱖ⫹1 Mean (⫾SD) Q score
p
Induced sputum
Spontaneous sputum
32 (65%) 27 (55%) ⫹0.47 (⫾1.39)
37 (74%) 33 (66%) ⫹0.78 (⫾1.34)
0.47 0.37 0.26
differences were not statistically significant (p ⫽ 0.37 and 0.26, respectively) (Table 2).
4. Discussion Collection of sputum is the only non-invasive procedure available to look for etiologic agents in tracheal, bronchial and pulmonary infections. Procedures such as protected brushing of the respiratory epithelium and protected bronchoalveolar lavage have a higher diagnostic yield since they bypass the oro-pharyngeal flora, but they are not used on a routine basis due to their cost and to the fact that they request trained personnel and are not totally innocuous (Chastre et al., 1988; Meduri et al., 1991; Torres et al., 1989). However, the collection of sputum is often disappointing; in the experience of our laboratory, 35– 45% of sputum specimens are heavily contaminated by saliva and unsuitable for culture. Aware of the literature on P. carinii pneumonia diagnosis (Leigh et al., 1989; Ng et al., 1989; Zaman et al., 1988), some physicians request sputum induction when they look for aerobic and facultative anaerobic bacteria. They consider that the procedure is easy and that even an hypothetical or marginal benefit is worthwhile in these conditions. Sputum induction is not without disadvantages. First, the procedure is time consuming: if some authors (Bigby et al., 1986; Metersky et al., 1998; Zaman et al., 1988) have used 5–15 min protocols for nebulization, others (Fishman et al., 1994; Miller et al., 1991) have proposed 20 –30 min and the total time requested for the procedure with a physical therapist can reach 45 min (Merrick et al., 1997). Combining a prolonged nebulization protocol and the use of experienced dedicated personnel brings the cost of a single induction to $29 (Merrick et al., 1997). Second, sputum induction can have adverse effects: in one study, 15% of the patients experienced nausea and vomiting, dyspnea or severe cough and 11% found the procedure unpleasant (Miller et al., 1991). We did not monitor the side-effects of sputum induction in our study. Finally, it is not impossible that hypertonic saline alters the viability of some pathogens, such as Streptococcus pneumoniae (Fishman et al., 1994). Our results confirm the findings of Fishman and colleagues (Fishman et al., 1994), saying that there is no advantage of sputum induction over the collection of spon-
213
taneously expectorated sputum before bacteriology workup. Sixty-five percent of patients who underwent aerosolization before collection produced good quality sputum versus 74% for spontaneous sputum when using the PMSs/ SECs ratio; with the Q score, the numbers were 55% and 66%, respectively. It is unlikely that we would have reached statistically significant results in favor of the induced sputum group with more patients, since the results were in fact slightly better in the spontaneous sputum group (statistically not significant). A strong point in Fishman’s (Fishman et al., 1994) prospective study is that both induced and spontaneous sputum were analyzed for each patient, but the fact that there was up to 48 h between the two examinations is a disadvantage of their protocol; in addition, they do not mention if the laboratory workers were blinded. The design of the study of Brandyopadhyay and colleagues ( Brandyopadhyay et al., 2000) was not comparable to ours since most of their induced patients had failed spontaneous sputum production before induction. These authors found that 69% of patients given nebulized saline could produce adequate samples. We think that our study, which is prospective, randomized and blinded, brings some new and useful insight on the topic. We deliberately chose realistic conditions applicable to most hospitals for the nebulization and sputum collection protocol: medium induction time (10 –15 min) and no special training for the nursing staff who was not supervised during the study. One can wonder if more stringent conditions would have yielded different results. Reviewing the P. carinii sputum induction literature (Birgy et al., 1986; Chouaid et al., 1993; Fishman et al., 1994; Metersky et al., 1998; Miller et al., 1990b; Miller et al., 1991; Ng et al., 1989; O’Brien et al., 1989; Zaman et al., 1988), we saw no clear relationship between the investment in time and specialized personnel and the results of the procedure. One study (Miller et al., 1991) showed that the use of physical therapists increases the number of successful attempts at sputum induction but does not increase the diagnostic yield. For induction before bacteriology work-up, direct comparison between simple and more demanding protocols remains to be done. The fact that we took specimen quality rather than culture results as an endpoint might be considered a limitation of our study. However, as the reliability of culture results directly depends on sputum quality, we doubt that a higher yield of culture after induction would be a convincing evidence of sputum induction. In conclusion, the use of sputum induction by hypertonic saline nebulization before bacteriology work-up does not appear to improve the quality of specimens in patients with productive cough, as judged by the ratio between PMNs and SECs on Gram stain. For that reason and because reports show that this procedure is costly and has potential sideeffects, its use should not be encouraged on a large scale, at least without close supervision and help of skilled personal.
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Acknowledgment This work was presented at the 38th Interscience Conference on Antimicrobial Agents and Chemotherapy, San Diego, 1998.
References Altai, S. S. (1993). Are sputum screens still relevant? Clin Microbiol Newslett, 15, 9. Bandyopadhyay, T., Gerardi, D. A., Metersky, M. L. (2000). A comparison of induced and expectroated sputum for the microbiological diagnosis of community acquired pneumonia. Resp, 67, 173–176. Beck, G. J., Nanda, K. (1962). Use of superheated saline aerosols as a diagnostic measure in pulmonary tuberculosis. Dis Chest, 42, 74 –78. Bigby, T. D., Margoleskee, D., Curtis, J. L., Michael, P. F., Sheppard, D., Hadley, W. K., Hopewell, P. C. (1986). The usefulness of induced sputum in the diagnosis of Pneumocystis carinii pneumonia in patients with the acquired immunodeficiency syndrome. Am Rev Respir Dis, 133, 515–518. Chastre, J., J. Y. Fagon, J. Y., Soler, P., Bornet, M., Domart, Y., Trouillet, J. L., Gilbert, C., Hance, A. J. (1988). Diagnosis of nosocomial bacterial pneumonia in intubated patients undergoing ventilation: Comparison of the usefulness of bronchoalveolar lavage and the protected specimen brush. Am J Med, 85, 499 –506. Chouaid, C., Housset, B., Poirot, J. L., Roux, P., Lebeau, B. (1993). Cost effectiveness of the induced sputum technique for the diagnosis of Pneumocystis carinii pneumonia (PCP) in HIV-infected patients. Eur Respir J, 6, 248 –252. Chuard, C., Reller, L. B. (1999). Diagnositic value of sputum and endotracheal suction aspirate Gram stain and culture in bacteremic pneumococcal pneumonia. Clin Microbiol Infect, 5, 106 –109. Fishman, J. A., Roth, R. S., Zanzot, E., Enos, E. J., Ferraro, M. J. (1994). Use of induced sputum specimens for microbiologic diagnosis of infections due to organisms other than Pneumocystis carinii. J Clin Microbiol, 32, 131–134. Jones, Jr., F. L., (1966). The relative efficacy of spontaneous sputa, aerosols-induced sputa, and gastric aspirates in the bacteriological diagnosis of pulmonary tuberculosis. Dis Chest, 50, 403– 408. Leigh, T. R., Parson, P., Hume, C., Husain, O. A., Gazzard, B., Collins, J. V. (1989). Sputum induction for diagnosis of Pneumocystis carinii pneumonia. Lancet, 2, 205–206. Meduri, G. U., Beals, D. H., Maijub, A. G., Baselski, V. (1991). Protected bronchalveolar lavage: A new bronchoscopic technique to retrieve
uncontaminated distal airway secretions. Am Rev Resp Dis, 143, 855– 864. Merrick, S. T., Sepkowitz, K. A., Walsh, J., Damson, L., McKinley, P., Jacobs, J. L. (1997). Comparison of induced versus expectorated sputum for diagnosis of pulmonary tuberculosis by acid-fast smear. Am J Infect Control, 25, 463– 466. Metersky, M. L., Alsenzadeh, J., Stelmach, P. (1998). A comparison of induced and expectorated sputum for the diagnosis of Pneumocystis carinii pneumonia. Chest, 113, 1555–1559. Miller, R. F., Leigh, T. R., Collins, J. V., Mitchell, D. M. (1990a). Tests giving an aetiological diagnosis in pulmonary disease in patients infected with the immunodeficiency virus. Thorax, 45, 62– 65. Miller, R. F., Semple, S. J. G., Kocjan, G. (1990b). Letter. Lancet, 1, 112. Miller, R. F., Kocjan, G., Buckland, J., Holton, J., Malin, A., Semple, S. J. G. (1991). Sputum induction for the diagnosis of pulmonary disease in HIV positive patients. J Infect, 23, 5–15. Morin, S., Tetrault, J., Kames, L., Hoppe-Bauer, J. E., Pezzlo, M. (1992). Specimen acceptability:evaluation of specimen quality. In Clinical Microbiology Procedures Handbook. Eds, HD Isenberg. Washington, DC: American Society for Microbiology, pp 1.3.1–1.3.6. Murray, P. R., Washington, J.A. (1975). Microscopic and bacteriologic analysis of sputum. Mayo Clin Proc, 50, 339 –344. Ng, V. L., Gartner, I., Weymouth, L. A., Goodman, C. D., Hopewell, P. C., Hadley, W. K. (1989). The use of mucolysed induced sputum for the identification of pulmonary pathogens associated with human immunodeficiency virus infection. Arch Pathol Lab Med, 113, 488 – 493. O’Brien, R. F., Quinn, J. L., Miyahara, B. T., Lepoff, R. B., Cohn, D. L. (1989). Diagnosis of Pneumocystis carinii pneumonia by induced sputum in a city with moderate incidence of AIDS. Chest, 95, 136 –138. Penn, R. L., Silberman, R. (1984). Effect of overnight refrigeration on the microscopic evaluation of sputum. J Clin Miocrobiol, 19, 161–163. Shata, A. M., Coulter, J. B., Parry, C. M., Chin’ani, G., Broadhead, R. L., Hart, C. A. (1996). Sputum induction for the diagnosis of tuberculosis. Arch Dis Child, 74, 535–537. Torres, A., Puig de la Bellacasa, J., Xaubet, A., Gonzalez, J., RodriquezRoisin, R., Jimenez de Anta, N. T., Agusti Vidal, V. A. (1989) Diagnostic value of quantitative cultures of bronchoalveolar lavage and telescoping plugged catheters in mechanically ventilated patients with bacterial pneumonia. Am Rev Respir Dis, 140, 306 –310. Van Scoy, R. E. (1977). Bacterial sputum cultures - a clinician’s viewpoint. Mayo Clin Proc, 52, 39 – 41. Yue, W. Y., Cohen, S. S. (1967). Sputum induction by newer inhalation methods in patients with pulmonary tuberculosis. Dis Chest, 51, 614. Zaman, M. K., Wooten, O. J., Suprahmanya, B., Ankobiah, W., Finch, P. J. P., Kamholz, S. L. (1988). Rapid non invasive diagnosis of Pneumocystis carinii from induced liquefied sputum. Ann Intern Med, 109, 7–10.
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Effect of sputum induction by hypertonic saline on specimen quality Christian Chuarda,b,*, Dominique Fracheboudb, Claude Regameya a Department of Medicine, Hoˆpital Cantonal, Fribourg, Switzerland Clinical Microbiology Laboratory, Hoˆpital Cantonal, Fribourg, Switzerland
b
Received 30 October 2000; accepted 15 March 2001
Abstract Microbiologic work-up of expectorated material is routinely used to search for the etiology of pulmonary infections, but sputum is often contaminated by saliva. Inhalation of hypertonic saline induces bronchial secretions and theoretically may improve specimen quality. We compared in a laboratory-blinded, randomized study the quality of sputum obtained either with induction by saline or without induction in patients with respiratory tract infection and a history of productive cough. The quality of sputum was considered good if the polymorphonuclear neutrophils (PMNs)/squamous epithelial cells (SECs) ratio was ⱖ2 or the Q (quality) score was ⱖ⫹1 on Gram stain. Forty-nine and 50 patients were able to expectorate in the induced and spontaneous sputum groups, respectively. PMNs/SECs ratio was ⱖ2 in 65% and 74% of the patients in the induced and spontaneous sputum groups (p ⫽ 0.47); for the Q score, a value ⱖ⫹1 was found in 55% and 66% of the patients of each group (p ⫽ 0.37). In conclusion, sputum induction by hypertonic saline inhalation does not improve specimen quality as judged by the PMNs/SECs ratio on Gram stain. © 2001 Elsevier Science Inc. All rights reserved.
1. Introduction Gram staining and culture of sputum is the straightest, least demanding way to search for the etiology of lower respiratory tract infections. Although these methods have been criticized for their lack of sensitivity and specificity (Altai, 1993; Chuard et al., 1999), they remain the standard microbiology exams in the field of pulmonary medicine. Unfortunately, bronchial secretions often are contaminated by saliva containing oro-pharyngeal flora. This contamination can be quantified on Gram-stained sputum by counting the number of polymorphonuclear leukocytes (PMNs) and squamous epithelial cells (SEQs) (Morin et al., 1992; Murray & Washington, 1975; Van Scoy, 1977), hence allowing to assess the quality of the specimen and to decide if further processing is relevant. In cases where bronchial or alveolar exudate production is scarce, the relative importance of contamination of sputum by saliva is greater. Inhalation of hypertonic saline irritates the airways and induces bronchial secretions; the hypertonicity of the saline also draws water into the bronchial lumen from the interstitial fluid by osmo-
* Corresponding author. Tel.: ⫹41-26-426-74-82; fax: ⫹41-26-42672-44. E-mail address: [email protected] (C. Chuard).
sis (Miller et al., 1990a). Theoretically, sputum induction is a potential means of improving specimen quality. Sputum induction has been extensively studied for the diagnosis of Pneumocystis carinii pneumonia with divergent results. While some authors reported a sensitivity of 77% to 98% compared with bronchoalveolar lavage (Leigh et al., 1989; Ng et al., 1989; Zaman et al., 1988), others could only obtain sensitivity results between 13% and 27% (Chouaid et al., 1993; Miller et al., 1990b; Miller et al., 1991). A study comparing induced sputum and spontaneous sputum found no difference between the procedures (Metersky, Alsenzadeh & Stelmach, 1998). Sputum induction is also fraught with controversy for the diagnosis of pulmonary tuberculosis (Beck & Nanda, 1962; Jones, 1966; Shata et al., 1996; Yue & Cohen, 1967). Two studies directly comparing induced and spontaneous sputum (Fishman et al., 1994; Merrick et al., 1997) reported similar yields with both methods. Surprisingly, although most sputum microbiology requests concern routine bacteriology, and not search for P. carinii or mycobacteria, we are aware of only two publications addressing the issue of the utility of sputum induction when looking for aerobic and facultative anaerobic bacteria. In a first study, Fishman and colleagues (Fishman et al., 1994) found no advantage to use induction as a routine procedure by comparing patients for the number of PMNs
0732-8893/01/$ – see front matter © 2001 Elsevier Science Inc. All rights reserved. PII: S 0 7 3 2 - 8 8 9 3 ( 0 1 ) 0 0 2 3 1 - 0
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C. Chuard et al. / Diagnostic Microbiology and Infectious Disease 39 (2001) 211–214
on Gram stain and for bacteriology culture results. On the contrary, the procedure was found useful in a very recent study by Bandyopadhyay and colleagues (Bandyopadhyay, Gerardi & Metersky, 2000) who investigated the role of induction in patients who were not able to produce sputum spontaneously. Because the literature on the utility of sputum induction for bacteriology work-up is so scarce and because this procedure is time-consuming and inconvenient for patients, we thought it would be worthwhile to address the issue in a new, comparative, blinded study. We prospectively compared the quality of sputum sent to the microbiology laboratory for Gram staining and bacterial culture when it was collected either with or without induction by hypertonic saline. Quality was assessed by evaluating the ratio between PMNs and SECs on Gram-stained specimens.
2. Materials and methods During the 1996 –1997 and 1997–1998 winters, patients hospitalized in the Department of Medicine of the Hoˆpital Cantonal, Fribourg, Switzerland, who were diagnosed with a lower respiratory tract infection, who had a history of productive cough and for whom the attending physician requested bacteriology work-up were eligible for the study. The Hoˆpital Cantonal de Fribourg is a 400-bed community hospital. When bacteriology work-up is requested, the microbiology laboratory performs a Gram stain, a culture for aerobic and facultative anaerobic bacteria and antimicrobial susceptibility testing. One hundred and twenty patients were randomized in two group: in the first group (n ⫽ 58), sputum was to be collected after induction by inhalation of 3% saline from an ultrasonic nebulizer for 10 –15 min (induced sputum); in the second group (n ⫽ 62), sputum was to be collected without induction (spontaneous sputum). The specimens were obtained by nurses who were not given special training; they had written instructions requesting that they teach patients and help them if necessary. No mouth rinse was performed before sputum collection and no chest percussion was used. If several sputum specimens were collected for a patient, only the first one was included in the study. Sputum was collected in sterile containers, stored at 4°C, transported to the microbiology laboratory within 20 h (Penn & Silberman, 1984) and processed by experienced technologists who were unaware of the mode of collection (laboratory-blinded design). The most purulent part of the sputum was Gram-stained and the number of PMNs and SEQs was recorded. The quality of the sputum was judged on the relative numbers of PMNs and SECs per field (low power magnification[10x]), using 2 methods: the simple ratio (PMNs/SECs) and the Q (quality) score. The Q score (Table 1), rated on a 7-point scale (-3 to ⫹3), is a more subtle way to evaluate the PMNs to SECs ratio and was chosen because it is proposed in a major clinical microbi-
Table 1 Calculating the Q score The Q score is calculated by adding the Q value obtained for polymorphonuclear neutrophils (PMNs) to the Q value obtained for squamous epithelial cells (SECs) PMNs per microscope fielda
Q value
0 1–9 10–24 ⱖ25
0 ⫹1 ⫹2 ⫹3
SECs per microscope fielda
Q value
0 1–9 10–24 ⱖ25
0 ⫺1 ⫺2 ⫺3
a
Low power magnification [10⫻] Adapted with permission from Morin et al. 1992
ology procedure manual (3). The quality of the sputum was considered good if the PMNs/SECs ratio was ⱖ2 or the Q score was ⱖ⫹1. Differences in proportions were analyzed using the 2 test, with Yates’ correction when appropriate. Analysis of variance (ANOVA) was used for comparing means. All tests were two-tailed. The p values less than 0.05 were regarded as significant.
3. Results During the study period, 120 patients were randomized: 58 in the induced sputum group and 62 in the spontaneous sputum group. It was possible to collect sputum from 49 patients (84.5%) in the induced sputum group and 50 patients (80.6%) in the spontaneous sputum group. In the induced sputum group, 24 patients (49%) were males, with a mean age ( ⫾ SD) of 68.5 ( ⫾ 17.1) years; 22 had pneumonia, 22 had bronchitis and 5 suffered from bronchiectasis or cystic fibrosis. In the spontaneous sputum group, 27 patients (54%) were males, with a mean age ( ⫾ SD) of 67.3 ( ⫾ 17.8) years; 29 had pneumonia, 18 had bronchitis and 3 suffered from bronchiectasis or cystic fibrosis. There were no statistically significant differences between groups for demographic characteristics or sputum production. A PMNs/SECs ratio ⱖ2 (good quality sputum) was found in 32 patients (65%) in the induced sputum group and in 37 patients (74%) in the spontaneous sputum group. This difference was not statistically significant (p ⫽ 0.47) (Table 2). A Q score ⱖ⫹1 was noted in 27 (55%) patients in the induced sputum group and in 33 patients (66%) in the spontaneous sputum group. The mean ( ⫾ SD) Q score was ⫹0.47 ( ⫾ 1.39) in the induced sputum group and ⫹0.78 (⫾ 1.34) in the spontaneous sputum group. These
C. Chuard et al. / Diagnostic Microbiology and Infectious Disease 39 (2001) 211–214 Table 2 Sputum quality with and without saline induction Patient group
PMNs/SECs ⱖ2 Q score ⱖ⫹1 Mean (⫾SD) Q score
p
Induced sputum
Spontaneous sputum
32 (65%) 27 (55%) ⫹0.47 (⫾1.39)
37 (74%) 33 (66%) ⫹0.78 (⫾1.34)
0.47 0.37 0.26
differences were not statistically significant (p ⫽ 0.37 and 0.26, respectively) (Table 2).
4. Discussion Collection of sputum is the only non-invasive procedure available to look for etiologic agents in tracheal, bronchial and pulmonary infections. Procedures such as protected brushing of the respiratory epithelium and protected bronchoalveolar lavage have a higher diagnostic yield since they bypass the oro-pharyngeal flora, but they are not used on a routine basis due to their cost and to the fact that they request trained personnel and are not totally innocuous (Chastre et al., 1988; Meduri et al., 1991; Torres et al., 1989). However, the collection of sputum is often disappointing; in the experience of our laboratory, 35– 45% of sputum specimens are heavily contaminated by saliva and unsuitable for culture. Aware of the literature on P. carinii pneumonia diagnosis (Leigh et al., 1989; Ng et al., 1989; Zaman et al., 1988), some physicians request sputum induction when they look for aerobic and facultative anaerobic bacteria. They consider that the procedure is easy and that even an hypothetical or marginal benefit is worthwhile in these conditions. Sputum induction is not without disadvantages. First, the procedure is time consuming: if some authors (Bigby et al., 1986; Metersky et al., 1998; Zaman et al., 1988) have used 5–15 min protocols for nebulization, others (Fishman et al., 1994; Miller et al., 1991) have proposed 20 –30 min and the total time requested for the procedure with a physical therapist can reach 45 min (Merrick et al., 1997). Combining a prolonged nebulization protocol and the use of experienced dedicated personnel brings the cost of a single induction to $29 (Merrick et al., 1997). Second, sputum induction can have adverse effects: in one study, 15% of the patients experienced nausea and vomiting, dyspnea or severe cough and 11% found the procedure unpleasant (Miller et al., 1991). We did not monitor the side-effects of sputum induction in our study. Finally, it is not impossible that hypertonic saline alters the viability of some pathogens, such as Streptococcus pneumoniae (Fishman et al., 1994). Our results confirm the findings of Fishman and colleagues (Fishman et al., 1994), saying that there is no advantage of sputum induction over the collection of spon-
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taneously expectorated sputum before bacteriology workup. Sixty-five percent of patients who underwent aerosolization before collection produced good quality sputum versus 74% for spontaneous sputum when using the PMSs/ SECs ratio; with the Q score, the numbers were 55% and 66%, respectively. It is unlikely that we would have reached statistically significant results in favor of the induced sputum group with more patients, since the results were in fact slightly better in the spontaneous sputum group (statistically not significant). A strong point in Fishman’s (Fishman et al., 1994) prospective study is that both induced and spontaneous sputum were analyzed for each patient, but the fact that there was up to 48 h between the two examinations is a disadvantage of their protocol; in addition, they do not mention if the laboratory workers were blinded. The design of the study of Brandyopadhyay and colleagues ( Brandyopadhyay et al., 2000) was not comparable to ours since most of their induced patients had failed spontaneous sputum production before induction. These authors found that 69% of patients given nebulized saline could produce adequate samples. We think that our study, which is prospective, randomized and blinded, brings some new and useful insight on the topic. We deliberately chose realistic conditions applicable to most hospitals for the nebulization and sputum collection protocol: medium induction time (10 –15 min) and no special training for the nursing staff who was not supervised during the study. One can wonder if more stringent conditions would have yielded different results. Reviewing the P. carinii sputum induction literature (Birgy et al., 1986; Chouaid et al., 1993; Fishman et al., 1994; Metersky et al., 1998; Miller et al., 1990b; Miller et al., 1991; Ng et al., 1989; O’Brien et al., 1989; Zaman et al., 1988), we saw no clear relationship between the investment in time and specialized personnel and the results of the procedure. One study (Miller et al., 1991) showed that the use of physical therapists increases the number of successful attempts at sputum induction but does not increase the diagnostic yield. For induction before bacteriology work-up, direct comparison between simple and more demanding protocols remains to be done. The fact that we took specimen quality rather than culture results as an endpoint might be considered a limitation of our study. However, as the reliability of culture results directly depends on sputum quality, we doubt that a higher yield of culture after induction would be a convincing evidence of sputum induction. In conclusion, the use of sputum induction by hypertonic saline nebulization before bacteriology work-up does not appear to improve the quality of specimens in patients with productive cough, as judged by the ratio between PMNs and SECs on Gram stain. For that reason and because reports show that this procedure is costly and has potential sideeffects, its use should not be encouraged on a large scale, at least without close supervision and help of skilled personal.
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Acknowledgment This work was presented at the 38th Interscience Conference on Antimicrobial Agents and Chemotherapy, San Diego, 1998.
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