G Dear, DM Uguccioni, JA Dovenbarger, ED Thalmann, E Cudahy, E Hanson, Dept. of Anesthesia and Divers Alert Network, Dept. of Community and Family Medicine Division of Occupational Medicine, Duke University Medical Center, Durham NC 27710; Naval Submarine Medical Research Laboratory (NSMRL), Groton CT., 06349.
Introduction: The incidence of decompression illness (DCI) in recreational divers is difficult to determine because the total number of dives performed each year is not known, and must be estimated.
Methods: DAN, in conjunction with NSMRL, sent surveys to 3,000 randomly selected DAN members. Some 1,654 were returned and analyzed, of which 1,628 contained information on diving activity and DCI for the last five years. The number of dives reported was from logs, memory, a combination of the two or estimated.
Results: Dives from logs, memory, or both had medians estimated from log normal distributions fitted to cumulative frequency plots by eye. Data are given in table. About 75% of responders were male accounting for 82% of dives, the 25% females accounted for 18% of dives. The median for logged dives was similar for males and females but the male median was slightly higher in the other two categories. Fifty-seven divers reported 67 cases of DCI (4.3% of females, 1.06% of dives; 3.3% of males, 5.3% of dives), but only 30 cases were reported as treated. The median number of dives for divers reporting DCI was similar for treated and untreated cases, ~25.2. Whether untreated cases were actually DCI is unknown, but if they aren't, DCI incidence would be only 1.51.
Conclusion: Total DCI incidence, assuming untreated cases were DCI, is close to Bove's (3.41) for sport divers but above that for military divers (2.65) (Undersea Hyper Med 1998;25:175-178). If the survey population of DAN members is assumed to be representative of the larger population then an average of 1,006 cases of DCI/year, reported to DAN from 1992-1997, at 3.38 DCI/104 dives would represent 2.98 million recreational dives/year. Whether untreated cases represent underreporting or false positives is unknown.