We selected 37 wards in three public and four private hospitals: medical (n = 15), surgical (n = 14), and obstetric (n = 8). Overall, 786 patients were included on the day of the cross sectional method. Eight were excluded because they were still present on day 30, precluding the review of their medical records. The three methods were therefore applied to 778 patients: 278 in medicine, 263 in surgery, and 237 in obstetrics. The adverse event rates found by the prospective and retrospective methods were similar and the point prevalence obtained by the cross sectional method was about one third lower than that of the other two methods (). The incidence of preventable adverse events assessed prospectively was 25% higher than that assessed retrospectively.
Proportion of inpatients with at least one adverse event according to epidemiological method (n=778)
Thirteen of the 254 adverse events were excluded from the reference list and considered as false positives (12 of the adverse events identified by the cross sectional method, none by the prospective method, and one by the retrospective method). The final list comprised 241 adverse events in 174 patients (110/80 in medicine, 114/80 in surgery, and 17/14 in obstetrics). Of these 174 patients, 122 (70%) had one adverse event, 38 (22%) had two adverse events, and 14 (8%) had three adverse events (125 patients had at least one adverse event on the day of cross sectional data collection). The cross sectional method identified 39 (64%) of the medical cases, 32 (56%) of the surgical cases, and 5 (45%) of the obstetric cases, and, respectively, 18 (51%), 6 (27%), and 3 (43%) of the preventable ones (). None of the most serious adverse events were identified.
Venn diagrams showing number of cases identified by three methods of data collection. Cases in brackets not identified by cross sectional method as they were identified after first day of data collection
The prospective method identified 63 (79%) of the medical cases, 49 (61%) of the surgical cases, and 8 (57%) of the obstetric cases, and, respectively, 32 (74%), 12 (46%), and 4 (44%) of the preventable cases. The retrospective method identified 43 (54%) of the medical cases, 61 (76%) of the surgical cases, and 8 (57%) of the obstetric cases, and, respectively, 16 (37%), 12 (46%), and 3 (33%) of the preventable cases. The prospective method was significantly more effective than the retrospective method at identifying cases in medicine (paired χ2 = 8.64, P < 0.01) and tended to be less effective at identifying cases in surgery (paired χ2 = 3.24, P < 0.07). The prospective method was significantly more effective at identifying preventable cases in medicine (paired χ2 = 3.0, P < 0.005) but no difference was observed in surgery. In obstetrics, effectiveness was not different but there were too few adverse events to draw conclusions.
When the medical and surgical cases were aggregated, the prospective and retrospective methods showed similar effectiveness (70% and 66% of 160 patients identified, respectively), but the prospective method was more effective at identifying preventable cases (64% and 40% of 71 patients, respectively; P < 0.02). Effectiveness was similar for adverse events occurring during hospital stay (68% and 64% of 110 patients), those responsible for hospital admissions (63% and 59% of 75 patients), and the most serious events (44% and 33% of 52 patients).
Reliability of cases identified among the 145 cases detected on the first day of study was good (global agreement 91.7%; κ = 0.83, 95% confidence interval 0.67 to 0.99), but agreement about preventability was low (67.8%; κ = 0.31, 0.05 to 0.57).
The workload for the prospective and cross sectional methods was perceived as similar, as the phase considered most time consuming for the staff was detection on the first day of data collection (average three hours in wards with 25 patients). Workload was perceived as less for the retrospective method but not negligible, especially when the information sources were multiple and the search was performed by the secretarial staff. The hospital staff constantly preferred the cross sectional and prospective methods because of their pedagogical and communicative virtues.