LOS ANGELES — Is misclassification of people who inject drugs (PWID) and are hospitalized because of infections affecting the analysis of outcomes from medications for opioid-use disorder (MOUD?

New research led by the David Geffen School of Medicine at UCLA and the Greater Los Angeles VA Healthcare System suggested that might be the case.

“Many studies used International Classification of Diseases (ICD) codes to identify PWID, although these may be misclassified and thus, inaccurate,” the authors wrote in Open Forum Infectious Diseases. “We hypothesized that bias from misclassification of PWID using ICD codes may impact analyses of MOUD outcomes.”1

To determine whether that is the case, the study team analyzed a cohort of 36 868 cases of patients diagnosed with Staphylococcus aureus bacteremia at 124 VHA hospitals between 2003 and 2014. To identify PWID, the researchers implemented an ICD code-based algorithm and a natural language processing (NLP) algorithm for classification of admission notes. They also analyzed outcomes of prescribing MOUD as an inpatient using both approaches. Defined as the primary outcome was 365-day all-cause mortality

NLP identified 2,389 cases as PWID, while ICD codes identified 6,804 cases as PWID. In the cohort identified by NLP, receipt of inpatient MOUD was associated with a protective effect on 365-day survival (adjusted hazard ratio, 0.48; 95% confidence interval, 0.29-.081; P < 0.01) compared with those not receiving MOUD. On the other hand, there was no significant effect of MOUD receipt in the cohort identified by ICD codes (adjusted hazard ratio, 1.00; 95% confidence interval, 0.77-1.30; P = 0.99).

“MOUD was protective of all-cause mortality when NLP was used to identify PWID, but not significant when ICD codes were used to identify the analytic subjects,” the authors pointed out.


  1. Goodman-Meza D, Goto M, Salimian A, Shoptaw S, Bui AAT, Gordon AJ, Goetz MB. Impact of Potential Case Misclassification by Administrative Diagnostic Codes on Outcome Assessment of Observational Study for People Who Inject Drugs. Open Forum Infect Dis. 2024 Jan 16;11(2):ofae030. doi: 10.1093/ofid/ofae030. PMID: 38379573; PMCID: PMC10878055.