Human coronaviruses (HCoVs) have been considered to be relatively harmless respiratory pathogens in the past. However, after the outbreak of the severe acute respiratory syndrome (SARS) and emergence of the Middle East respiratory syndrome (MERS), HCoVs have received worldwide attention as important pathogens in respiratory tract infection. This review focuses on the epidemiology, pathogenesis and clinical characteristics among SARS-coronaviruses (CoV), MERS-CoV and other HCoV infections.

The resistance rate of 67 Mycoplasma pneumoniae isolates from 356 ambulatory adult patients with respiratory tract infection was 69% (46 of 67). All 46 macrolide-resistant strains harbored point mutations in the 23S ribosomal RNA gene. Patients infected with macrolide-resistant M. pneumoniae required significantly longer durations of antibiotic therapy and had longer time to resolution of fever.

Macrolide resistance rates of Mycoplasma pneumoniae in the Beijing population were as high as 68.9%, 90.0%, 98.4%, 95.4%, and 97.0% in the years 2008 to 2012, respectively. Common macrolide-resistant mobile genetic elements were not detected with any isolate. These macrolide-resistant isolates came from multiple clones rather than the same clone. No massive aggregation of a particular clone was found in a specific period. Mycoplasma pneumoniae is one of the important pathogens causing human respiratory tract infection, especially in community-acquired pneumonia (1, 2). The major clinical treatment for M. pneumoniae infection is the use of macrolide antibiotics (ML). With the widespread use of the drug, ML-resistant isolates have been reported worldwide (3-5). The resistance mechanism has been identified as a point mutation in the 23S rRNA gene. Other mechanisms of macrolide resistance cannot be excluded and have not been identified. In recent years, ML-resistant M. pneumoniae has become very serious in Asia (6, 7) and has attracted the attention of scientists. Studies on ML-resistant M. pneumoniae in China have only recently been conducted, and the limited reports have been mainly ML resistance analyses of a small number of strains isolated during a few months and from specific populations, such as children or adults (8-11). These reports are lacking continuous full-population surveillance data of M. pneumoniae drug resistance. In view of the above-mentioned information, we have studied drug resistance of 309 M. pneumoniae isolates from a whole population of strains isolated from people with respiratory infections in Beijing, China, from 2008 to 2012, a study which will help us to understand the status of drug-resistant M. pneumoniae in Beijing in recent years.M. pneumoniae strains. A total of 309 M. pneumoniae strains were isolated from 1,183 respiratory infection specimens from Beijing Chao-Yang Hospital, Beijing Children's Hospital, and Beijing Centers for Diseases Control and Prevention. One hundred fifty-six isolates were from 388 pediatric specimens of patients Ͻ14 years of age, and the remaining 153 isolates were collected from 795 adolescent and adult specimens. All 309 isolates were purified, cultured, and identified with a real-time PCR method (12).Detection of macrolide resistance at the gene level. Genomic DNA of 309 M. pneumoniae isolates was extracted using the QIAamp DNA minikit (Qiagen). The extracts were distributed into aliquots and saved at Ϫ20°C. The domain V region of the 23S rRNA gene was amplified by PCR methods described previously (6). The amplification products were sequenced by the Beijing Genomics Institute (BGI). The results showed that there were existing point mutations in domain V of the 23S rRNA gene region of 280 strains in the 309 M. pneumoniae isolates. In 272 of the 280 isolates (97.1%), the mutation was identified as A2063G. Seven of the 280 isolates (2.5%) had the A2064G mutation, one of the 280 isolates (0.4%) had an A2063T mutation, and the remaining 29 isolates did not h...