Background Community acquired pneumonia (CAP) is one of the most common infectious disease in emergency department.In 2005 the concept of healthcare associated pneumonia (HCAP) was proposed by the ATS/IDSA guidelines.The clinical features and microbiology of HCAP are different from CAP,however,the initial antimicrobial treatment is still controversial.We aimed to compare the clinical efficacy between HCAP patients treated initially with HCAP guidelineconcordant antimicrobial agents and those with CAP guideline-concordant antimicrobial agents.Methods We conducted a retrospective observational study on HCAP patients who were admitted to emergency department between December 2011 and December 2012.Patients were divided into 2 groups according to their different initial antimicrobial treatment.We compared clinical features,distribution of pathogen,severity,days and spending on intravenous antimicrobial,length and charge of hospitalization and clinical outcomes,and meanwhile analyzed the clinical efficacy as well.Results Of the 125 HCAP patients,55 patients received CAP guideline-concordant antimicrobial agents and 70 received HCAP agents.The major pathogens were Klebsiella pneumoniae,methicillin-resistant staphylococcus aureus (MRSA),Pseudomonas aeruginosa and Escherichia coll The 2 groups were similar at baseline,including old age,comorbidities,Pneumonia Severity Index scores,APACHE scores,and length of intravenous antimicrobial use and hospitalization duration,and in-hospital mortality.Overall efficacy rate occurred in 70.0％ of HCAP agent patients and 50.9％ of CAP agent patients (P=0.029).Antimicrobial charge and total hospital charge for HCAP agent patients were significantly higher than that for CAP agent patients.Conclusions Initial treatment of HCAP patients in emergency department with HCAP guideline-concordant antimicrobial could increase clinical efficacy rate,as well as antimicrobial charge and total hospital charge,but was not associated with shortening the length of stay,or lowering in-hospital mortality.