Abstract
Prior antibiotic use, contamination, limited blood volume, and processing delays reduce yield of blood cultures for detection of Streptococcus pneumoniae. We performed immunochromatographic testing (ICT) on broth from incubated blood culture bottles and real-time lytA polymerase chain reaction (PCR) on broth and whole blood and compared findings to blood culture in patients with suspected bacteremia. We selected 383 patients in Mali and 586 patients in Thailand based on their blood culture results: 75 and 31 were positive for pneumococcus, 100 and 162 were positive for other pathogens, and 208 and 403 were blood culture negative, respectively. ICT and PCR of blood culture broth were at least 87% sensitive and 97% specific compared with blood culture; whole blood PCR was 75–88% sensitive and 96–100% specific. Pneumococcal yields in children < 5 years of age increased from 2.9% to 10.7% in Mali with > 99% of additional cases detected by whole blood PCR, and from 0.07% to 5.1% in Thailand with two-thirds of additional cases identified by ICT. Compared with blood culture, ICT and lytA PCR on cultured broth were highly sensitive and specific but their ability to improve pneumococcal identification varied by site. Further studies of these tools are needed before widespread implementation.
Highlights
IntroductionPneumonia is a leading cause of child morbidity and mortality worldwide.[1,2] Clinical trials of pneumococcal conjugate vaccines (PCV) have shown that Streptococcus pneumoniae is responsible for 20–37% of chest X-ray positive pneumonia in children < 5 years of age.[3,4,5] Etiological diagnosis of bacterial pneumonia relies primarily on blood culture that yields a positive result in 5–10% of hospitalized patients; a subset of these are identified as pneumococcus.[6,7,8] Several factors reduce the sensitivity of blood culture, including small blood volumes, antibiotic pretreatment, specimen contamination by other organisms because of poor specimen collection or processing technique, prolonged transport time, and inconsistent availability of supplies
Pneumococcal yields in children < 5 years of age increased from 2.9% to 10.7% in Mali with > 99% of additional cases detected by whole blood polymerase chain reaction (PCR), and from 0.07% to 5.1% in Thailand with two-thirds of additional cases identified by immunochromatographic testing (ICT)
From a total of 5,086 patient blood cultures obtained in Mali between January 25, 2010 and January 24, 2011, we selected 383 (7.5% of total, 90.9% < 5 years of age) for inclusion based on their blood culture findings: 75 positive controls, 100 negative controls, 10 alarm-positive, subculture-negative cases, and 198 alarm-negative cases
Summary
Pneumonia is a leading cause of child morbidity and mortality worldwide.[1,2] Clinical trials of pneumococcal conjugate vaccines (PCV) have shown that Streptococcus pneumoniae is responsible for 20–37% of chest X-ray positive pneumonia in children < 5 years of age.[3,4,5] Etiological diagnosis of bacterial pneumonia relies primarily on blood culture that yields a positive result in 5–10% of hospitalized patients; a subset of these are identified as pneumococcus.[6,7,8] Several factors reduce the sensitivity of blood culture, including small blood volumes, antibiotic pretreatment, specimen contamination by other organisms because of poor specimen collection or processing technique, prolonged transport time, and inconsistent availability of supplies. These factors are common in resource-poor settings.[9,10,11] even under optimal conditions, blood cultures identify only 30% of suspected cases of pneumococcal pneumonia,[5,12] limiting the ability of surveillance to accurately estimate disease burden and evaluate the impact of vaccines
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