Critically Appraised Topic:
What is the risk of HIV seroconversion after occupational exposure and is this modified by post-exposure prophylaxis with zidovudine?
Date: Jan 8, 1998
Appraised by Deb Bynum, MD
Clinical Bottom Lines:
1. Significant risk factors for seroconversion included deep injury, injury with a device that was visibly contaminated with source patient’s blood, procedure involving a needle placed in the source patient’s artery or vein, and exposure to a source patient who died of AIDS within two months.
2. By univariate analysis, there was no significant difference between case patients and controls inuse of zidovudine after exposure (9 of 33 case patients (27%), 247 of 679 controls (36%), Odds ratio 0.7, p=.35); no evidence that case patients were more or less likely than controls to be offered zidovudine (83% cases offered prophylaxis, 79% controls offered, p=1.0).
3. After control for the risk factors found associated with HIV transmission, no differences were detected in the rates at which case patients and controls were offered post-exposure prophylaxis with zidovudine (OR .92, p=.90); however, case patients were significantly less likely to have taken prophylaxis than controls (OR=.19, p=.003) after controlling for risk factors.
4. Among workers who took zidovudine, 67% of controls and 89% of case patients (p=.28) had their first dose within 4 hours after exposure; There were no differences between cases and controls in the duration or dose of zidovudine.
The Evidence: Case-control study of health care workers with occupational, percutaneous exposure to HIV infected blood (cases had HIV seroconversion temporally associated with exposure, controls were workers who remained HIV seronegative despite exposure); Total of 33 case patients and 679 controls were included.
| Risk factor: | Adjusted OR (95% CI) |
| Deep injury | 15 (6.0-41) |
| Visible blood on device | 6.2 (2.2-21) |
| Procedure involving needly in artery or vein | 4.3 (1.7-12) |
| Terminal illness in source patient | 5.6 (2.0-16) |
| Post-exposure use of zidovudine | 0.19 (.06-.52) |
| (all risk factors were significant with p<.01) | |
| number of risk factors | Case patients | Controls | Unadjusted OR | ||
| Total | prophylaxis | Total | prophylaxis | ||
| 0 | 0 | ----- | 128 (40%) | 40 (31%) | ---- |
| 1 | 3(11%) | 0 | 124 (39%) | 51 (41%) | .20 |
| 2 | 11 (41%) | 2 (18%) | 55 (17%) | 33 (60%) | .15 |
| 3 | 8 (30%) | 1 (12%) | 12 (4%) | 7 (58%) | .10 |
| 4 | 5 (19%) | 5 (100%) | 1 (0.3)% | 0 | .33 |
| Total | 27 (100%) | 8 (30%) | 320 (100%) | 131 (41%) | .61 (p=.31) |
Comments:
1. Observation that there was no difference in zidovudine use among cases and controls in an unadjusted analysis is likely due to confounding -- zidovudine use was more likely among patients after exposure characterized by one of the four risk factors, and risk factors were more prevalent among case patients than controls. Therefore case patients had more serious exposures than controls and with adjustment for risk factors, case patients were significantly less likely than controls to have taken zidovudine (OR .19, p=.003).
2. Retrospective case-control design not optimal to assess efficacy of zidovudine, but prospective placebo controlled trial not possible and this data agrees with prior observations of efficacy of prophylaxis
3.limited due to small number of case patients
4. potential for reporting bias and ascertainment bias (more likely to report exposure or identify exposure as more significant if exposure was one perceived to have higher risk or if information obtained after case patient seroconverted)
Sources:
Cardo, DM et al. A Case-Control Study of HIV Seroconversion in Health Care Workers. NEJM 1997: 337: 1485-90.
Cardo, DM et al. A Case-Control Study of HIV Seroconversion in Health Care Workers After Percutaneous Exposure. N Engl J Med 1997; 337: 1485-90.