Background International guidelines recommend the systematic screening for Neisseria gonorrhoeae (NG) and Chlamydia trachomatis (CT) infections in all men who have sex with men (MSM) who have engaged in unprotected sex. However, the optimal screening strategy remains unclear. We developed a modeling approach to optimize NG/CT screening strategy in MSM. Methods A compartmental model of NG/CT screening and infection was implemented. NG/CT anal, pharyngeal, and urine (APU) samples from MSM attending the sexually transmitted infections clinic were used to estimate the screening rate, prevalence, and incidence in a base case scenario. Different screening strategies (scenarios; S) were then evaluated: APU samples every 12 months (S1); APU samples every 3 months (S2); APU samples every 6 months (S3); anal and pharyngeal (AP) samples every 6 months (S4); and AP samples every 3 months (S5). Results We analyzed 2973 triplet APU samples from 1255 patients. We observed 485 NG and 379 CT diagnoses. NG/CT prevalence and incidence estimates were 12.0/11.1% and 40/29 per 100 person-years, respectively, in the base case scenario. As compared to S2, the reference strategy, the proportions of missed NG/CT diagnoses were 42.0/41.2% with S1, 21.8/22.5% with S3, 25.6/28.3% with S4, and 6.3/10.5% with S5, respectively. As compared to S2, S1 reduced the cost of the analysis by 74%, S3 by 50%, S4 by 66%, and S5 by 33%. The numbers needed to screen for catching up the missed NG/CT diagnoses were 49/67 with S1, 62/82 with S3, 71/87 with S4, and 143/118 with S5. Conclusions S5 appears to be the best strategy, missing only 6.3/10.5% of NG/CT diagnoses, for a cost reduction of 33%.

dDisk diffusion testing is widely used to detect methicillin resistance in staphylococci, and cefoxitin is currently considered the best marker for mecA-mediated methicillin resistance. In low-inoculum diffusion testing (colony suspension at 10 6 CFU/ml), the addition of moxalactam in combination with cefoxitin has been reported to improve on cefoxitin alone for the detection of methicillin-heteroresistant staphylococci. However, moxalactam is absent from EUCAST and CLSI guidelines, which use highinoculum diffusion testing (colony suspension at 10 8 CFU/ml), calling into question the potential interest of including moxalactam in their recommendations. The inhibition zone diameters of cefoxitin and moxalactam, alone and in combination, were evaluated for concordance with mecA and mecC positivity in a large collection of clinical Staphylococcus isolates (611 Staphylococcus aureus, Staphylococcus lugdunensis, and Staphylococcus saprophyticus isolates and 307 coagulase-negative staphylococci other than S. lugdunensis and S. saprophyticus isolates, of which 22% and 53% were mecA-positive, respectively) and in 25 mecC-positive S. aureus isolates using high-inoculum diffusion testing. Receiver operating characteristic, sensitivity, and specificity analyses indicated that the detection of mecA-and mecC-positive and negative isolates did not improve with moxalactam, either alone or in combination with cefoxitin, compared to cefoxitin alone. These findings were similar in both the S. aureus/S. lugdunensis/S. saprophyticus group and in the coagulase-negative staphylococci group. Our results do not support the use of moxalactam as an additional marker of methicillin resistance when testing with high-inoculum disk diffusion.