Introduction

Blood cultures are of limited utility in nonsevere community-acquired pneumonia, though routinely recommended for severe community-acquired pneumonia or health care-associated pneumonia due to perceived greater bacteremia risk, particularly with multidrug-resistant organisms. The utility of this practice is unknown.

Methods

In this observational cohort study, we abstracted data from medical records for consecutive hospitalizations for pneumonia by adults to an academic medical center from 2014-2015. The primary outcomes included bacteremia, multidrug-resistant organism bacteremia, and appropriate management changes attributed to culture results, stratified by pneumonia classification (nonsevere community-acquired pneumonia, severe community-acquired pneumonia, or health care-associated pneumonia) and likelihood the bacteremia was due to pneumonia vs another infection. We assessed the diagnostic test performance of one or more guideline-defined risk factors for bacteremia in nonsevere community-acquired pneumonia, for whom cultures are routinely recommended.

Results

Of 456 pneumonia hospitalizations, 30 (6.6%) had bacteremia, with a greater incidence in severe community-acquired pneumonia (14.7%) than nonsevere community-acquired pneumonia (7.8%) and health care-associated pneumonia (6.6%; P = .12). Seventeen bacteremia cases were likely due to pneumonia (3.7%). Only 2 (0.4%) had multidrug-resistant organisms (both health care-associated pneumonia), one of whom was due to pneumonia. Appropriate management changes occurred in 8 cases (1.8%; 7 de-escalation and 1 escalation of antibiotics); only 1 with bacteremia likely due to pneumonia (de-escalation). The one case of appropriate antibiotic escalation occurred in a patient with vancomycin-resistant Enterococcus unrelated to pneumonia. Having one or more guideline-defined risk factors did not identify bacteremia in nonsevere community-acquired pneumonia (positive likelihood ratio, 1.10; 95% confidence interval, 0.61-1.99).

Conclusion

Routine blood cultures in pneumonia have extremely low yield and utility irrespective of severity and risk.

Germline-expressed endogenous small interfering RNAs (endo-siRNAs) transmit multigenerational epigenetic information to ensure fertility in subsequent generations. In Caenorhabditis elegans, nuclear RNAi ensures robust inheritance of endo-siRNAs and deposition of repressive H3K9me3 marks at target loci. How target silencing is maintained in subsequent generations is poorly understood. We discovered that morc-1 is essential for transgenerational fertility and acts as an effector of endo-siRNAs. Unexpectedly, morc-1 is dispensable for siRNA inheritance but is required for target silencing and maintenance of siRNA-dependent chromatin organization. A forward genetic screen identified mutations in met-1, which encodes an H3K36 methyltransferase, as potent suppressors of morc-1(-) and nuclear RNAi mutant phenotypes. Further analysis of nuclear RNAi and morc-1(-) mutants revealed a progressive, met-1-dependent enrichment of H3K36me3, suggesting that robust fertility requires repression of MET-1 activity at nuclear RNAi targets. Without MORC-1 and nuclear RNAi, MET-1-mediated encroachment of euchromatin leads to detrimental decondensation of germline chromatin and germline mortality.