To the best of our knowledge, this is a relatively comprehensive study which contributes to the prevalence, risk factors, phenotypic and molecular characteristics for S. aureus nasal carriage among community-based drug users in China. The prevalence of S. aureus carriage in the study (15.01%) is lower than previously reported estimates ranged from 19.79–45.05% [4, 8–11]. Participants of those previous studies were injection drug users. In this study, however, only 64.02% of participants had history of using injection drugs in the past 3 months. Additionally, we found that a majority of long-term drug users who took drugs by snorting had few vibrissae. This might also be a potential factor leading to a low prevalence of S. aureus carriage. Further studies need to be conducted in the future. The prevalence of MRSA nasal carriage (6.80%) in the study is similar to the afore mentioned studies in other countries [4, 12–14]. Notably, the proportion of MRSA in S. aureus isolates were higher than the observed studies [4, 14].
In this study, we found that current cohabitation was a risk factor for S. aureus carriage in drug users, which is different from another study [4]. One of the possible reasons might be that most drug users cohabitated with other drug users. This could provide more opportunities for sharing drugs [11]. HIV infection has been reported to be a risk factor for S. aureus carriage [15], however, we did not find any significance in this study. This could be caused by the limited number of drug users with HIV infection. Therefore, further studies need to be carried out to identify the risk factors for S. aureus carriage in drug users.
The patterns of antibiotic resistance on S. aureus isolates are consistent with limited available studies [8, 16, 17], with high proportions of penicillin, erythromycin, clindamycin and tetracycline resistance. The proportions of antibiotic resistance were higher in MRSA isolates than MSSA isolates, which is also observed in other studies [8, 17]. Teicoplanin has been widely used as an anti-MRSA agent in infectious patients in the past decades [18, 19], which can partially explain the high proportion of teicoplanin resistance in MRSA isolates. The proportion of MDR MRSA (70.83%) is high. The most predominant MDR pattern could partially demonstrate the high use of antibiotics in community-based drug users and provide evidence that healthcare workers need to be more careful with selection of antibiotics for drug users. The high proportions of erythromycin and tetracycline resistance and low proportions of erythromycin- and tetracycline-resistance genes could demonstrate that resistant genes are always attributed to the presence of antibiotic resistance.
The proportions of virulence genes were high in MRSA, suggesting the higher risks of MRSA isolates in casing virulence-related diseases, including Staphylococcal scalded skin syndrome, toxic shock syndrome, Staphylococcal food poisoning, etc. [20–22]. The proportions of virulence genes for MRSA isolates were higher than the observed studies [6, 23–25]. The results implied that drug users with MRSA carriage harbouring virulence associated genes, might have higher risks for relevant disease and should draw more attention.
The results of CCs and STs for S. aureus isolates could demonstrate the multiple transmissions among human beings, livestock and environment, which are similar to previous studies [6, 23]. We found high proportions of ST5 and ST59 in this study and these STs were also globally reported in communities [26]. We also found hospital- (ST188) [27, 28] and livestock- (ST398) [29, 30] associated STs in this study. Additionally, according to the results of SCCmec types we could also know the source of MRSA isolates were from both communities and healthcare settings, which is similar to the observed studies [4, 9]. MRSA isolates could circulate between communities and healthcare settings and this might be a potential risk for other populations. Therefore, relevant decolonization methods could be taken for drug users with MRSA carriage, which would help prevent further MRSA circulation.
Our study contributes to the prevalence, risk factors, phenotypic and molecular characteristics for S. aureus carriage, particularly MRSA carriage, among drug users in China. Despite the strengths of this study, there are several limitations. First, it was a cross-sectional study. Thus, we could not determine the persistence of S. aureus carriage. Secondly, we only collected nasal swabs instead of nasopharyngeal swabs, which may lead to underestimation of the prevalence of S. aureus carriage. Thirdly, we did not collect information whether male participants were those who have sex with men due to confidentiality. We will explore it in future research. Finally, the generality of this study is limited owing to the small number of drug users.