bacterial parapneumonic pleural effusion ( ppe ) accounts for 40% of community - acquired pneumonia cases and has high morbidity and mortality ( 1 ) .
a study in the uk showed that the mortality rate of bacterial ppe was 15% and 20% of patients needed to be hospitalized for several months ( 2 ) .
an early identification of the causative pathogen cultured from pleural samples can improve the treatment outcomes by indicating the appropriate antibiotics as well as treatment interventions such as surgical drainage ( 4 , 5 ) .
the use of blood culture bottles for ascites fluid or joint fluid gave a better yield of causative agents than did the standard culture bottle ( 6 , 7 ) .
similar results were obtained in a study to detect bacteria in pleural fluid in the uk .
the blood culture bottle method increased the pathogen identification rate by 20.8% compared with sterile culture bottles in 53 bacterial ppes ( 8) .
pathogens of pneumonia , causes of ppe , may be different between asian and the western countries ( 9 , 10 ) . the northeastern parts of thailand and australia have a higher incidence of melioidosis or burkholderia pseudomallei infection ( 11 ) .
there are limited data of using blood culture bottles to yield the identification of bacterial pathogens in asian patients with bacterial ppes .
the aim of this study was to compare the culture - positive rate by the blood culture bottles and the standard culture bottles in bacterial ppes in different settings and larger study populations from the original study ( 8) .
patients diagnosed with bacterial ppe in khon kaen hospital , khon kaen , thailand , were enrolled consecutively and prospectively . the study period was from june first , 2012 to december 31st , 2013 .
the inclusion criteria were patients aged > 18 years and with exudative , neutrophilic ppe .
the patients were excluded if causes other than bacterial pleural effusion were suspected including the presence of lymphocytes in the pleural fluid at levels of more than 50% , the presence of abnormal cells , lung abscesses , or bloody pleural effusions ( 13 ) .
pleural fluids of all the eligible patients were collected in blood culture bottles in addition to standard culture bottles to compare the organism identifications in both bottles . in this practice ,
a standard culture bottle is a sterile bottle without any media ; 5 ml pleural fluid was put in both culture bottles .
blood culture bottles were bact / alert fa for aerobic organisms , containing soybean - casein digestive broth , sodium polyanethol sulfonate , pyridoxal hcl , menadione , hemin , activated charcoal , l - cysteine , carbohydrate , and amino acids ( biomerieux , inc . ,
blood culture bottles were used for aerobic organisms because aerobic organisms are the common pathogens in bacterial ppe ( 8) , and patients with pleural effusion from anaerobic pathogens were excluded .
the blood culture bottles were incubated in bact / alert system at 35c for seven days ( 15 , 16 ) , and the procedures for bact / alert system were followed ( 16 ) , while pleural fluids in the standard culture bottles or sterile tubes were cultured using blood , macconkey , and chocolate media .
baseline patient characteristics , laboratory results , and culture results were collected and compared with the disease severity .
the culture results using blood culture bottles and standard culture bottles were compared using descriptive statistics .
the disease severity was classified into the most severe empyema thoracis , complicated ppe , and simple ppe as the least severity ( 17 ) . in brief ,
empyema thoracis is diagnosed if the pleural fluid is purulent , while complicated ppe is warranted if one of the following features is met ; positive pleural fluid smears for bacterial pathogens ; pleural fluid glucose < 60 mg / dl , pleural fluid ph < 7.20 , or loculated pleural effusion .
simple ppe is exudative , neutrophilic pleural effusion without evidence of complicated ppe and negative pleural fluid culture by bacterial culture in both types of culture bottles .
( 8) , the proportions of the bacteria - positive pleural fluid cultures by blood culture bottles ( 58.5% ) and standard culture bottles ( 37.7% ) methods were used for sample size determination .
the sample size was calculated by the differences of both mentioned proportions with a two - tailed , confidence level of 95% , power of 80% , and deviation of 15% by the mcnamar s method .
the main primary outcome of the study was the comparison of the culture - positive rates between the blood culture bottles and the standard culture bottles groups .
descriptive statistics were used to calculate means , standard deviation ( sd ) , and proportions . comparing the proportions between the groups
statistical analyses were executed by stata 10.0 ( college station , texas , usa ) .
during the study period , 169 patients were suspected of bacterial ppe . of those ,
40 were excluded due to either lymphocytic pleural effusion ( 33 patients ) or transudative pleural effusion ( seven patients ) . in total , 129 patients ( 76.3% ) met the study criteria ; 80 ( 62.0% ) with empyema thoracis ; 19 ( 14.7% ) with complicated ppe and 30 ( 23.3% ) with simple ppe . among these three levels of severity ,
baseline characteristics such as age , gender , and co - morbid diseases were comparable ( table 1 ) . the pleural fluid features and peripheral blood analysis among these three groups
data are presented as mean ( sd ) , median ( range ) , or number ( percentage ) ; alcohol consumption is more than 10 g / d .  
data are presented as median ( first - third quartile ) unless indicated otherwise .  
there was a statistically significant difference between the bottle types , p value < 0.001 ( p value for all other pairs > 0.05 ) .
the results of the previous study ( 8) wherein the blood culture bottle , specifically bact / alert fa increased the bacterial identification rates in ppe , were confirmed .
this study was different from the original study in terms of the study location ( the uk vs an asian tropical country ) , the sample size ( 53 vs 129 ) , plus different possible organisms in the effusion .
the overall bacterial identification rate in bacterial ppe by blood culture bottle in this study was 24.0% and even higher at 33.8% in the empyema group .
previous antibiotic use in this study population ( 79.1% ) , as shown in table 1 ( 18 ) , and delayed transport process to the culture lab ( 19 ) might also be considered as factors . the culture - positive rate by blood culture bottle in the study , however , was still higher than a previous report by ferrer at 15.0% ( 20 ) .
better bacterial culture yield for pleural effusion using blood culture bottles may be due to using charcoal - containing medium , while the standard culture bottles do not have such medium ( 14 ) .
charcoal may increase the oxygenation , resulting in a higher rate of organism recovery . in this study , the most common pathogen in the pleural fluid was streptococcus sp .
burkholderia pseudomallei , the causative agent of melioidosis , was found in five patients ( 31 patients , 16.1% in our study ) .
reechaipichitkul ( 12 ) reported pleural effusion in 12.2% and 15.3% of cases with acute and subacute / chronic pulmonary melioidosis , respectively .
s. pneumoniae is usually the most common pathogen causing community - acquired pneumonia , but was not found in this study .
this may also be explained by the high rate of previous antibiotic use ( 79.1% ) .
the main limitation of this study was that the size of the study population was somewhat lower than the calculated power sample size ( 126 vs. 135 subjects ) .
the results , however , showed statistically significant advantages of the blood culture bottle method over the standard culture bottle method for the detection of bacteria in pleural effusion . the relatively low bacterial detection rate for the pleural fluid may be due to the high rate of previous antibiotic use .
the results of this study strongly supported the previously report of menzies et al . using a relatively larger sample size ( 8) .
blood culture bottle method should be used in routine clinical practices for pathogen identification in pleural fluids of patients suspected of bacterial ppe . in conclusion ,
the blood culture bottle method was more effective than the standard culture bottle method for the detection of bacterial pathogens in ppe .
 background : bacterial parapneumonic pleural effusions ( ppes ) have high morbidity 
 . the accurate identification of pathogens is vital for initiating the appropriate treatment . 
 a previous study suggested that the use of blood culture bottles might improve the bacterial yield in ppes.objectives:the aim of this study was to compare the culture positivity rate by the blood culture bottles and the standard culture bottles in bacterial ppes.patients and methods : patients diagnosed with ppes at the khon kaen hospital , khon kaen , thailand , which is an endemic area of melioidosis , were enrolled consecutively and prospectively . 
 the study period was from june first , 2012 to december 31st , 2013 . 
 the inclusion criteria were adult patients aged > 18 years , with exudative , neutrophilic parapneumonic effusion . 
 of the pleural fluid samples , 5 ml from all the eligible patients were collected in both blood culture bottles and the standard culture bottles . 
 patient baseline characteristics , laboratory results , and culture results were collected and analyzed.results:during the study period , 129 patients met the study criteria . 
 the bacteria - positive rate of pleural fluid culture using the standard culture bottle was 14.0% , whereas the positive rate using blood culture bottles was 24.0% ( p 
 < 0.001).conclusions : the blood culture bottle method is more effective than the standard culture bottle method for the detection of bacterial pathogens in ppe . 
1. Background
2. Objectives
3. Patients and Methods
4. Results
5. Discussion