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Patients with chronic ITP may have increased infection risk before diagnosis
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Patients with primary chronic immune thrombocytopenia have an increased risk for infections up to 5 years before diagnosis, according to results of an epidemiological study.
Primary immune thrombocytopenia (ITP) is a rare hematologic disorder with an expected annual incidence of 3.3 per 100,000 people worldwide.
Previously, the estimated incidence for adult chronic ITP ranged from 1.6 to 3.9 per 100,000 people; however, in 2009 the International ITP Working Group modified the definition of chronic ITP as a disease persistent for more than 12 months, instead of 6 months as originally defined.
Charlotta Ekstrand, a graduate student of the Centre for Pharmacology at Karolinska Institutet, and colleagues used the Swedish Patient Register to estimate the incidence of chronic ITP under the new definition.
Further, it is known that infections can cause autoimmune diseases, but the understanding of this mechanism is limited. Therefore, Ekstrand and colleagues also sought to examine the incidence of infections before diagnosis of chronic ITP.
Of the 3,121 patients diagnosed with ITP between 2006 and 2012, 1,087 patients were diagnosed with incident chronic ITP (men, n = 531; women, n = 556). The observed annual incidence of chronic ITP was 2.3 per 100,000 people (95% CI, 2.15-2.45).
Of this cohort, 23% of the men and 21% of the women had at least one hospital visit for infection within 5 years prior to their diagnosis. The standardized incidence ratios (SIR) to estimate relative risks for diagnosis of infection was 8.74 (95% CI, 7.47-10.18), or 11.14 (95% CI, 8.81-13.9) in women and 7.36 (95% CI, 5.91-9.05) in men.
Patients with chronic ITP had an increased risk for viral infections (SIR = 17.72, 95% CI, 10.67-27.68), fungal infections (SIR = 77.26, 95% CI, 47.17-119.32), skin infections (SIR = 27.74, 95% CI, 15.51-45.76), sexually transmitted diseases (SIR = 211.56, 95% CI, 109.19-369.58), urinary tract infection (SIR = 7.3. 95% CI, 5.61-9.34) and gastrointestinal infections (SIR = 6.54, 95% CI, 4.38-9.40) before diagnosis of ITP.
Higher-magnitude SIRs occurred specifically for candidiasis (SIR = 77.08, 95% CI, 44.03-125.18), viral infection of unspecified site (SIR = 11.98, 95% CI, 5.97-21.44) and acute upper respiratory infections of multiple and unspecified sites (SIR = 12.86, 95% CI, 7.49-20.59).
Chronic ITP also appeared associated with an increased risk for receiving antibacterial and antiviral treatments before diagnosis (SIR = 1.37, 95% CI, 1.25-1.5). Researchers observed the highest magnitude of SIRs for amoxicillin (SIR = 1.59, 95% CI, 1.19-2.1), macrolides (SIR = 1.69, 95% CI, 1.24-2.24), nitrofurantoin (SIR = 1.52, 95% CI, 1.04-2.15) and direct acting antivirals (SIR = 1.54, 95% CI, 1-2.28).
The researchers acknowledged their study may have been limited because patients with increased susceptibility to infections may have frequent healthcare contacts and laboratory investigations. Further, they did not have access to primary care data, where the majority of infections are diagnosed.
“The findings indicate that infection is not only related to the immunomodulation treatment but also to the disease itself,” Ekstrand and colleagues wrote. – by Kristie L. Kahl
Disclosure: The researchers report no relevant financial disclosures.
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