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11 février, 2008 16:09

MEMPHIS, Feb. 8 -- Lymphopenia -- not neutropenia -- is a risk factor for respiratory syncytial virus-related lower respiratory tract infections in immunocompromised children, researchers said here.

• Explain to interested patients that respiratory syncytial virus (RSV) is a common cause of respiratory infections in children and in immunosuppressed patients can be serious and even fatal.
• Note that progression to the more severe lower respiratory tract infections is more common during periods of severe immunosuppression, in children receiving chemotherapy, and in recipients of stem cell transplants.
• Explain that this study identifies two factors -- age and lymphopenia -- that can help predict which children are at risk of progression to more severe disease.

A second independent risk factor is age, Aditya Gaur, M.D., of St. Jude Children's Research Hospital, and colleagues reported in the February issue of Pediatrics. Children under the age of two are more likely to develop such infections.

The findings could help guide diagnosis and treatment of lower respiratory tract infections caused by respiratory syncytial virus (RSV), Dr. Gaur and colleagues wrote.

The first finding is especially important, Dr. Gaur said, because oncologists are used to relying on neutrophil counts to decide if a child is at risk for infection.

"With cancer patients, clinicians are used to identifying those at risk for bacterial and fungal infections based on a patient having neutropenia," Dr. Gaur said.

The study was a single-institution retrospective look at patients younger than 21 with neoplasias, hematologic disorders, immunodeficiency syndromes, or hematopoietic stem cell transplants who tested positive for RSV between January 1997 and April 2005.

The study period covered eight successive RSV winter seasons, the researchers said, and 58 patients met the study criteria.

For this study, neutropenia was defined as an absolute neutrophil count of no more than 500 cells per cubic millimeter and profound neutropenia as a count of no more than 100 cells.

Lymphopenia was defined as an absolute lymphocyte count of no more than 300 cells per cubic millimeter and profound lymphopenia as no more than 100.

RSV disease location was defined as either upper or lower respiratory tract, and patients with both were analyzed in the second category, Dr. Gaur and colleagues said.

All told, 16 patients -- or 27.6% -- met the criteria for a lower respiratory tract infection at some point during the course of their illness.

The study found that:

• 42% of patients with hematopoietic stem cell transplants, AML or SCIDS and 36.4% with solid tumors developed lower respiratory tract infections, compared with only two of 23 ALL patients (or 8.7%).
• 14.6% of patients older than two developed lower respiratory tract infections, compared with 58.8% of those two or younger.
• 60% of those with profound lymphopenia developed lower respiratory tract infections, compared with 20.8% of those who were not lymphopenic.

In univariate analysis, those three factors were significant, but in a multivariate analysis, only age and lymphopenia remained significant predictors of RSV-related lower respiratory tract infection, the researchers said.

Patients ages two or younger had an odds ratio for lower respiratory tract infection of 9.84, with a 95% confidence interval from 1.95-49.8, compared with older children.

And those with profound lymphopenia had an odds ratio for lower respiratory tract infection of 7.17, with a 95% confidence interval from 1.17 to 44.03, compared with those who were not lymphopenic.

"The new information is important because it helps identify children who are most at risk for severe disease using easily available clinical information," Dr. Gaur said.

"This narrows down the patient population that needs to be considered for antiviral therapy, which is costly and often inconvenient to receive from a child's perspective," he said.

El Saleeby CM, et al "Risk factors for severe respiratory syncytial virus disease in children with cancer: the importance of lymphopenia and young age"Pediatrics 2008; 121: 235-243.

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