Abstract and Introduction
Objectives: To determine a quantitative herpes simplex virus (HSV) DNA threshold in lower respiratory tract specimens that correlates with positive viral culture and clinical outcomes.
Methods: Bronchoalveolar lavage and bronchial wash samples from 53 HSV culture-positive and 61 culture-negative matched controls were tested using HSV-1 and HSV-2 quantitative polymerase chain reaction (qPCR).
Results: Median viral culture turnaround time was 21.8 days and 9.9 days for culture-negative and culture-positive specimens, respectively. Using an HSV-1 viral load threshold of 1.62 × 103 copies/mL, there was 93% agreement with viral culture. An HSV-1 viral load ≥1.3 × 104 copies/mL was associated with worse clinical outcome compared to a viral load <1.3 × 104 copies/mL (hazard ratio [HR] = 4.27, P = .017), and there was a trend of worse outcome compared to patients with undetectable HSV-1 DNA (HR = 1.60, P = .056).
Conclusions: qPCR has clinical utility for rapid accurate identification of HSV-1 in lower respiratory tract specimens.
Debate continues as to whether the detection of herpes simplex virus (HSV) in lower respiratory tract specimens, especially from immunosuppressed, critically ill patients, and organ transplant recipients, represents a true clinical infection requiring therapy or innocuous viral shedding secondary to severe underlying illness.[1–4] Moreover, rendering a confident clinical diagnosis of HSV pneumonia is challenging, particularly because many patients lack easily detectable herpetic lesions, radiographic and bronchoscopic findings are nonspecific, and clinical interpretations are frequently complicated by superimposed coinfections.[5–8] The morphologic and immunohistochemical evaluation of cellular material for the cytopathic effect of HSV, using bronchoalveolar lavage (BAL) cytology or lung biopsy specimens performed for another reason, constitutes the gold standard for HSV diagnosis due to the high specificity, but suffers from poor sensitivity. In many medical centers, the preferred method for identifying HSV in BAL specimens has become viral culture. Conventional viral culture, however, has a lengthy turnaround time (TAT) and is thus not the ideal diagnostic modality for guiding therapeutic decisions in critically ill patients.
Detection of HSV in the lower respiratory tract is further complicated by the nonuniformity of lavage specimens. BAL cellularity is affected by environmental exposures and underlying disease, as well as operator experience and technique.[10–12] Unlike HSV viremia, where the diagnosis is dependent on the detection of cell-free viral DNA in plasma, the diagnosis of HSV-associated lower respiratory tract infections requires the detection of cell-associated viruses. Indeed, HSV has been detected by immunohistochemistry in alveolar macrophages and pulmonary epithelial lining cells in patients who died from acute respiratory distress syndrome or pneumonia; no extracellular virus was observed.
In this study, we determined a quantitative threshold of HSV DNA in lower respiratory tract specimens that correlated with positive viral culture and clinical outcome. We also investigated the utility of quantitative polymerase chain reaction (qPCR) for a housekeeping gene to account for differences in the cellularity of the lower respiratory tract specimens. Finally, we evaluated the relationship between the HSV viral load and clinically relevant outcomes.
Am J Clin Pathol. 2018;150(6):522-532. © 2018 American Society for Clinical Pathology