Doctors at the Centers for Disease Control and Prevention and Michigan public health officials said Friday they are trying to determine whether West Nile virus can be transmitted in breast milk after a lactating mother was confirmed with the disease.
CDC West Nile expert Dr. Lyle Petersen told a conference call a 40-year-old Michigan mother who delivered her baby Sept. 2 was confirmed with the mosquito-borne disease Thursday but so far the infant has shown no symptoms.
Petersen said tests on the mother's milk have indicated there is evidence of West Nile virus but it is unclear whether it is live virus and capable of spreading the illness.
The mother was given two units of blood after she delivered her baby -- the first on Sept. 2 and the second on Sept. 3. Investigators are trying to determine whether the blood was the source of the infection. A second Michigan resident, a 47-year-old man who underwent a liver transplant and received multiple units of blood, also contracted West Nile. Both the man and the woman received blood from a common donor.
Jesse Goodman, deputy director for the Center for Biologic Evaluation and Research, said these latest cases appear to be more evidence that West Nile can be transmitted through blood products.
"We are considering whether and when we may need to take additional steps (to protect the nation's blood supply)," Goodman said. "We really had concluded blood transmission was very likely and we have been acting on that conclusion. ... One of the most important things now is that we are urgently working with manufacturers and with others on potential blood screening tests to try to facilitate their availability."
The latest human cases are among the 2,206 that have been confirmed this year. Some 108 people have died nationwide.
Dr. Matthew Boulton, state epidemiologist with the Michigan Department of Community Health, said blood tests are being done on the infant to determine whether infection has occurred. Results are expected next week.
"From other countries where West Nile is endemic, we have no evidence West Nile can be transmitted via breast milk," Petersen said. "Where West Nile is endemic ... there's ongoing transmission to children via mosquito bite. That's going to be the most common route of transmission. It's hard to sort out. Mosquito bites would account for pretty much all infections in endemic countries. We need to study potential role of breast milk in the future."
Petersen said if a breastfeeding mother is concerned she has contracted West Nile disease, she should consult her doctor about whether to continue breastfeeding. He said the determining factor should be how ill the woman is, not the fact that she has West Nile.
Petersen said West Nile cases appear to have peaked in the South in August and within the last two weeks in the northern states.
Michigan is second only to Illinois in the number of overall cases and deaths. Michigan has reported 314 cases and 15 deaths; Illinois reported 573 cases and 32 deaths. Thirty-four of the cases in Illinois and 18 from Michigan have not yet been included in the CDC totals. Three of the Illinois deaths also have not been confirmed by the CDC.
