Human T Lymphotropic Virus Type 1 Infection. Part 2
Laboratory analysis. Serum HTLV‐1 antibody examination was performed using particle agglutination assays. The Serodia ATLA kit (Fujirebio) was used through April 1990, after which the Serodia HTLV‐1 kit (Fujirebio) was used.
Stored serum samples collected from all patients who developed gastric cancer underwent EIA (SRL) for detection of IgG antibodies to H. pylori. An IgG antibody titer of 10 U/mL was considered indicative of H. pylori. The samples were collected before the development of gastric cancer and the initiation of H. pylori eradication therapy.
A total of 296 of 994 individuals underwent a histologic examination, a 13C urea breath test, and, as described above, EIA for IgG antibodies to H. pylori. One hundred twenty (55 men and 65 women) of 497 examined patients were in the HTLV‐1–seropositive group, and 176 (71 men and 105 women) of 497 were in the HTLV‐1–seronegative group. H. pylori positivity was defined as a positive result of any of these assays.
Statistical analysis. The demographic characteristics of the study subjects were compared using the Student t test (for age and duration of follow‐up). The rate of H. pylori positivity was evaluated with the Fisher exact test. The cumulative incidence and survival rate for patients with gastric cancer were evaluated with the Kaplan‐Meier method and were compared using the log‐rank test. Odds ratios (ORs), their 95% confidence intervals (CIs), and statistical significance were computed. All analyses were performed with StatView, version 5.0.
Results
The rate of H. pylori positivity was 61.7% in the HTLV‐1–positive group, compared with 71.6% in the HTLV‐1–negative group. Among men, the rates were 56.4% in the HTLV‐1–positive group and 74.6% in the HTLV‐1–negative group, and among women, the rates were 66.2% and 69.5%, respectively.
There were 14 cases of gastric cancer (incidence, 2.8% [3.0 cases/year per 1000 population]) among HTLV‐1–positive patients and 35 cases (incidence, 7.0% [7.3 cases/year per 1000 population]) among HTLV‐1–negative control patients (OR, 0.38; 95% CI, 0.21–0.70). For men, there were 8 cases in the HTLV‐1–positive group and 19 cases in the HTLV‐1–negative group (OR, 0.39; 95% CI, 0.17–0.90), and for women, there were 6 and 16 cases, respectively (OR, 0.36; 95% CI, 0.14–0.91). The mean age at the time of gastric cancer onset was 72 years (range, 49–96 years) in the HTLV‐1–positive group, compared with 70 years (range, 42–77 years) in the HTLV‐1–negative group. In the HTLV‐1–positive group, there were 9 cases of intestinal‐type carcinoma, 2 cases of diffuse type, and 3 cases of unknown type, compared with 14 cases of intestinal‐type carcinoma, 15 cases of diffuse type, 1 case of mixed type, and 5 cases of unknown type in the HTLV‐1‐negative group. Eight (57.1%) of 14 patients in the HTLV‐1–positive group had been infected with H. pylori, compared with 27 (77.1%) of 35 patients in the HTLV‐1–negative group. The mean observation period (±SD) was years in the HTLV‐1–positive group and years in the HTLV‐1–negative group.