Kosloff et al. Chiropractic & Manual Therapies (2015) 23:19
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Table 4 Chiropractic and PCP visits prior to the index date (Commercial) Exposures All Age <45 yr
Age ≥ 45 yr
Cases (n = 1159)
Controls (n = 4633)
Cases (n = 98)
Controls (n = 392)
Cases (n = 1061)
Controls (n = 4241)
Most recent DC Visit 0-1 day: n (%)
3 (0.3) 6 (0.5) 8 (0.7) 9 (0.8) 19 (1.6)
11 (0.2) 21 (0.5) 31 (0.7) 44 (0.9) 62 (1.3) 15 (0.3) 41 (0.9) 93 (2.0) 165 (3.6) 316 (6.8)
* * * *
*
3 (0.3) 6 (0.6) 8 (0.8) 9 (0.8) 17 (1.6)
11 (0.3) 20 (0.5) 30 (0.7) 41 (1.0) 55 (1.3) 14 (0.3) 39 (0.9) 89 (2.1) 150 (3.5) 287 (6.8)
0-3 days: n (%) 0-7 days: n (%) 0-14 days: n (%) 0-30 days: n (%)
1 (0.3) 1 (0.3) 3 (0.8) 7 (1.8) 1 (0.3) 2 (0.5) 4 (1.0) 15 (3.8) 29 (7.4)
2 (2.0)
Most recent PCP Visit 1-1 day: n (%)
41 (3.5) 78 (6.7) 115 (9.9) 157 (13.5) 219 (18.9)
4 (4.1) 8 (8.2)
37 (3.5) 70 (6.6) 105 (9.9) 145 (13.7) 196 (18.5)
1-3 days: n (%) 1-7 days: n (%) 1-14 days: n (%) 1-30 days: n (%)
10 (10.2) 12 (12.2) 23 (23.5)
*Insufficient data to compute an estimate.
Discussion The primary aim of the present study was to investigate the association between chiropractic manipulative treat- ment and VBA stroke in a sample of the U.S. population. This study was modelled after a case – control design previ- ously conducted for a Canadian population [32]. Adminis- trative data for enrollees in a large national health care insurer were analyzed to explore the occurrence of VBA stroke across different time periods of exposure to chiro- practic care in comparison with PCP care. Unlike Cassidy et al. [32] and most other case – control studies [33,37,38], our results showed there was no sig- nificant association between VBA stroke and chiroprac- tic visits. This was the case for both the commercial and MA populations. In contrast to two earlier case – control studies [32,33], this lack of association was found to be Table 5 Chiropractic and PCP visits prior the index date (Medicare) Exposures Cases (n = 670) Controls (n = 2680) Most recent DC Visit 0-1 day: n (%) * 4 (0.1) 0-3 days: n (%) * 8 (0.3) 0-7 days: n (%) * 9 (0.3) 0-14 days: n (%) 1 (0.1) 15 (0.6) 0-30 days: n (%) 2 (0.3) 24 (0.9) Most recent PCP Visit 1-1 day: n (%) 16(2.4) 18 (0.7) 1-3 days: n (%) 30 (4.5) 36 (1.3) 1-7 days: n (%) 55 (8.2) 97 (3.6) 1-14 days: n (%) 90 (13.4) 183 (6.8) 1-30 days: n (%) 143 (21.3) 346 (12.9) *Insufficient data to compute an estimate.
irrespective of age. Although, our results (Table 8) did lend credence to previous reports that VBA stroke oc- curs more frequently in patients under the age of 45 years. Additionally, the results from the present study did not identify a relevant temporal impact. There was no significant association, when the data were sufficient to calculate estimates, between chiropractic visits and stroke regardless of the hazard period (timing of most recent visit to a chiropractor and the occurrence of stroke). There are several possible reasons for the variation in results with previous similar case – control studies. The younger (<45 yrs.) commercial cohort that received chiropractic care in our study had noticeably fewer cases. The 0 – 30 days hazard period included only 2 VBA stroke cases. There were no stroke cases for other hazard periods in this population. In contrast, earlier studies reported sufficient cases to calculate risk esti- mates for most hazard periods [32,33]. Another factor that potentially influenced the differ- ence in results concerns the accuracy of hospital claims data in the U.S. vs. Ontario, Canada. The source popula- tion in the Province of Ontario was identified, in part, from the Discharge Abstract Database (DAD). The DAD includes hospital discharge and emergency visit diagno- ses that have undergone a standardized assessment by a medical records coder [39]. To the best of our know- ledge, similar quality management practices were not routinely applied to hospital claims data used in sour- cing the population for our study. An additional reason for the disparity in results may be due to differences in the proportions of chiropractic visits where SMT was reportedly performed. Our study showed that SMT was not reported by chiropractors in more than 30% of commercial cases. It is plausible that a number of the cases in earlier studies also did not
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