Study Purpose A high number of post-transplant infections with respiratory symptoms remain unresolved, despite routine testing for the common respiratory viruses. Using an open metagenomic approach, we re-analyzed respiratory samples collected from symptomatic lung transplant patients for which no microbial etiology was found.

Methods For metagenomic sequencing, virus particles were enriched from respiratory swabs, total nucleic acids extracted and amplified randomly. Sequencing libraries were prepared with NexteraXT and sequenced on a MiSeq Illumina (1 x 150 bp). Quality filtered reads were cleaned from non-viral reads by an in-house bioinformatics pipeline and blastedagainst a database containing > 40'000 viral sequences.

Results Among 71 participants, 22 (31%) showed no respiratory symptoms up to 15 months after lung transplantation; 49 (69%) developed a total of 55 episodes with respiratory symptoms. In 26 (47%) episodes, no etiology of infection could be determined by routine diagnostics.

Analyzing 24 undetermined throat swabs, the metagenomic approach identified a viral etiology in 4 patients: Rhinovirus A (2), Rhinovirus B (1) and Coronavirus HKU (1). In 6 of the 24 samples we detected HHV-7. Using a more sensitive real-time PCR, 17 of 24 samples were positive for HHV-7. HHV-7 viral loads increased between transplantation and the first routine visit (after 4 – 6 weeks) in 6 out of 7 patients studied longitudinally. In addition, we frequently found Torque Teno virus and bacteriophage reads.

Conclusions Our metagenomic approach identified microbial pathogens in a single analysis. Our study revealed low-level infections with known respiratory viruses and additionally identified cases of HHV-7 infection. HHV-7 viral loads increased in lung transplant patients while under immunosuppression. The role of HHV-7 in this setting remains to be determined. No other viruses were found in the remaining symptomatic lung transplant patients leaving the exact etiology of infection unclear. This study highlights the potential of metagenomic sequencing in complex diagnostic situations such as immunocompromised hosts.

CITATION INFORMATION: Mueller N, Lewandowska D, Ruehe B, Schreiber P, Zagordi O, Geissberger F, Schuurmans M, Greiner M, Zbinden A, Boeni J, Benden C, Trkola A, Huber M. Resolution of Undefined Etiology of Respiratory Infections in Lung Transplant Patients with Unbiased Metagenomic Sequencing. Am J Transplant. 2016;16 (suppl 3).

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