Background Herpes simplex virus type-1 (HSV-1) has been described to cause respiratory tract infections in critically ill patients or in individuals that are immunocompromised. It is a continuing matter of debate under which circumstances HSV-1 is a relevant pathogen for pneumonitis. While its role during critical illness has been investigated by prospective interventional studies, comparatively little systematic data is available on the role of HSV-1 for pneumonitis in outpatients with autoimmune disease under a maintenance regimen of immunosuppression.

Methods We retrospectively reviewed the charts of ~1400 patients with rheumatoid arthritis, vasculitis, and systemic lupus erythematosus (SLE) that were followed at the outpatient clinic of a German University hospital during the years 2000–2007. Episodes of admission to a ward resulting in the diagnosis of pneumonia/pneumonitis were identified, and the type of pneumonia and clinical features retrospectively studied.

Results 63 patients with rheumatoid arthritis, vasculitis, or SLE were admitted to a ward and diagnosed to have pneumonia/pneumonitis. Using bronchoscopy a total of 6 cases of pulmonary infection associated with HSV-1 in the lower respiratory tract were identified. Among those, 2 cases suggested a causative role of HSV-1 as the sole agent causing pneumonitis that proved clinically responsive to antiviral treatment. In the remaining 4 cases HSV-1 appeared as a bystander of bacterial infection. Maintenance therapy with leflunomide, which inhibits HSV-1 assembly in vitro, was associated with a milder course of pneumonitis in one patient. Detection of HSV-1 was associated with stronger immunosuppressive regimens and vasculitic disease.

Conclusion The present study analyzed the frequency and hallmarks of cases of HSV-1 associated pneumonitis that occurred in a comparatively large cohort of patients with rheumatologic autoimmune diseases. In an area of controversy, this study provides further evidence that HSV-1 causes isolated pneumonitis in the immunocompromised. The study may provide an estimate on the frequency of relevant HSV-1 infection and bacterial agents in outpatients with autoimmune disease.