Background:

Influenza infection significantly impacts transplant patients. Despite this, there are limited data on how virological characteristics, including influenza viral load (VL), impact the outcome of infection.

Methods:

Transplant recipients with lab-confirmed influenza A infection were enrolled in a prospective multicenter cohort clinical study from 2010-15. Nasopharyngeal swabs were taken at diagnosis (day 0) and days 3, 6, 11, 18 and 28. Influenza VL (lower limit of detection (LOD) 10² copies/mL) was measured by real-time RT-PCR.

Results:

Serial swabs were available from 258 patients. Median age was 56 years (range 2-83). Transplant types were kidney (38%), lung (19%), liver (17%), heart (12%), and hematopoietic stem cell (HSCT) (14%). Pneumonia occurred in 21.9% of patients and 10.8% of all patients were admitted to the ICU. The majority (94.2%) of patients were treated with oseltamivir and death occurred in 5.4% of patients. The proportion of transplant recipients with a positive NP swab on days 0, 3, 6, 11, 18 and 28 was 87%, 76%, 45%, 25%, 7.1% and 0%, respectively. At days 0 and 3, median VLs were 1.3×10⁴ and 9.1×10², respectively. From day 6 to 28, the median VLs were below the LOD. HSCT recipients had significantly higher median VLs than SOT recipients at day 0 (1.0×10⁵ vs. 8.4×10³; p=0.001), day 3 (3.2×10³ vs. 7.9×10²; p=0.015) and day 6 (7.0×10² vs.<LOD; p=0.003). Transplant recipients who did not receive influenza vaccine within the same season as infection had a 7.6-fold higher median VL at day 0, compared to vaccinated (5.6×10⁴ vs. 7.4×10³; p=0.026). Those with pneumonia had significantly higher median VLs at days 0, 3, 6 and 11 (p<0.001). Interestingly, the day 0 VL for recipients who developed pneumonia was 39-fold higher than those that did not (2.9×10⁵ vs. 7.4×10³). Median VLs were higher at days 0 (p=0.0084), 3 (p=0.0049), 6 (p=0.021) and 11 (p=0.0049) among those admitted to the ICU.

Conclusion:

We provide unique insight into viral dynamics in transplant patients. Our study shows high influenza viral loads are associated with severity of illness and absence of previous vaccination.

CITATION INFORMATION: Ferreira V, Humar A, Cordero E, Blumberg E, Limaye A, Silveira F, Danziger-Isakov L, Levi M, Kalpoe J, Englund J, Multicenter Influenza Group M, Kumar D. Influenza Viral Dynamics in a Large Cohort of Transplant Patients with Natural Influenza Infection. Am J Transplant. 2017;17 (suppl 3).

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