After initial screening, the full text of 281 potentially eligible articles was
retrieved for detailed assessment, and 27 studies were eligible for analysis [3,6,8,9,19, 21-42]. All of the eligible studies presented OR for colorectal adenoma related to H. pylori infection. [3,6,8,9,19, 21-42] Nineteen of them are cross-sectional studies [3, 6, 8, 19, 21-24, 25-28, 30, 31,
35, 37-40], and the remaining eight are case-control studies [9, 29, 32-34, 36, 41,
42]. Serology was utilized as the detection method for H. pylori in 14 studies [8, 9, 21, 23, 25-27, 31-35, 38, 39], pathology in 4 [3, 22, 40, 42],
UBT in 4 [6, 37], CLO in 6 [19, 24, 30, 36], and combining UBT and CLO in 2 [28, 29].
Gender and age are reported in 22 [3,6,8,9,19, 21-30, 34-40] and 27 [3,6,8,9,19, 21-35,37-39,41,42]
studies respectively. Most studies were carried out in Asia (7 in Korea, 3 in Taiwan,
3 in Japan, 1 in Thailand and 1 in China) and the remaining in Americas (5 in USA
and 1 in Brazil) and in Europe (2 in Germany, 1 in Turkey, 1 in Greece and 1 in Israel).
All included studies had assessed the quality of all eligible studies using the ROBINS
I scale and no serious risk of bias after survey (in Appendix).
A flow chart describing the process of study selection is shown in Figure 1. For the
meta-analysis, data were extracted from twenty-seven studies with a total of 68,410
patients, and the pooled OR for colorectal adenoma related to H. pylori infection was 1.51 (95% CI 1.39–1.63), although there was significant heterogeneity
(p < 0.001) (Table 1 and Figure 2). Because of geographic and time differences in
DM prevalence rate [43-52], subgroup analysis for the studies was performed by classifying them into 4 groups:
group 1: DM prevalence < 6%; group 2: DM prevalence from 6 ~ 8%, group 3: DM prevalence
from 8~10% and group 4: DM prevalence > 10% (Table 1 and Figure 2).
In the subgroup analysis, the background population DM prevalence < 6% studies
had three studies with a total of 886 patients. Meta-analysis of these studies revealed
that the H. pylori-infected patients have an increased risk of having colorectal adenoma with a pooled
OR of 1.24 (95% CI 0.86–1.78) but no significant difference. There was no significant
heterogeneity in group 1 studies (p = 0.279). Since the study background population
DM prevalence increased more than 6%, the H. pylori-infected patients have significant increased risk of having colorectal adenoma. This upturn
was more significant when the background population DM prevalence was approximately
6% to 8%. After meta-analysis of these studies, the H. pylori-infected people had a higher risk of colorectal adenoma than noninfected people.
The pooled OR was 2.16 (95% CI 1.61–2.91), and a total of 11655 patients were included.
In these studies, Lin’s study noted the DM prevalence in his study participants, and
males had an 8.1% prevalence of DM, and females had a 6.1% prevalence of DM. Due to
Lin’s study population, 6.94% of patients had DM and were thus classified into group
2 for subgroup analysis. There was significant heterogeneity in the group 2 studies
(p < 0.01)
In groups 3 and 4, similar results were observed. Compared to that of group 2
studies, the pooled OR of groups 3 and 4 was mildly decreased but still had a significantly
elevated risk of colorectal adenoma in H. pylori-infected patients. For the H. pylori-infected patients, the risk of colorectal adenoma in group 3 was 1.40 (95% CI 1.24–1.57),
and the group 4 OR was 1.52 (95% CI 1.46–1.57). The group 3 studies included 28,431
patients, and the heterogeneity across studies was marginal (I2 = 58.6%, p = 0.013). There were 27,438 participants included in group 4 studies, and there was no significant
heterogeneity (I2 = 0.0%, p = 0.704). We also checked other variables, including gender, detection
methods of H. pylori infection and study designs, and there was no evidence of statistical relevance to
OR for adenoma with H. pylori infection.