Background Approximately 90% of the US population has protective levels of anti-tetanus-antibody (ATA). Elderly individuals demonstrate lower protective levels of ATA compared with the general population; decreased immune system function has been postulated. It is unknown if human immunodeficiency virus (HIV) infection is also associated with non-protective ATA.
Objective Determine if there is an association between CD4 counts and ATA in HIV-infected patients.
Methods A convenience sample of outpatients from 2 HIV specialty clinics was recruited from May 2000 until July 2004. ATA was measured by ELISA, and a level greater than 0.15 IU is considered protective. CD4 counts were measured by flow cytometry within 60 days of ATA testing. The lowest CD4 count documented in the clinic record was also documented (nadir CD4). For analysis, a CD4 count of<100 cells/μL was considered severe illness. Data were analyzed with standard parametric and non-parametric testing. Logistic regression models were developed to test association with tetanus protection.
Results 262 subjects were included with a mean age of 43 years (range 20 to 67 years). A total of 227/262 (87%) had protective ATA. The CD4 count for patients with protective ATA was 459 cells/μL compared to 353 cells/μL for nonprotective ATA (p = 0.055). When the nadir CD4 count was analyzed, patients with protective ATA had 208 cells/μL and nonprotective had 128 cells/μL (p = 0.006). Those with nadir CD4 counts<100 cells/μL were less likely to have protective ATA (86/106, 81%) than those with nadir counts ≥ 100 cells/μL (141/156, 90%, p = 0.03). After adjusting for factors that may influence ATA, including country of birth, logistic regression models found an association between lower CD4 and less tetanus protection trending toward significance for contemporaneous CD4 counts (p = 0.06). The adjusted association between ATA and CD4 was significant when nadir CD4 counts were analyzed (p = 0.01).
Discussion HIV-infected individuals have generally similar protection to tetanus as the general US population. However, among HIV patients, a history of lower CD4 counts is more often associated with non-protective tetanus titers. This suggests that in some patients the memory for this antigen is lost, particularly when CD4 counts drop below 100 cells/μL.
Conclusion Clinicians must be aware that HIV-infected patients with low CD4 counts may be at greater risk for non-protective ATA. Support received from North Shore-LIJ Research Institute, GCRC, Grant # M01 RR018535.
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