The Boston Globe reported today on the death of an 87-year-old man who passed away after suffering a Listeria infection he contracted from drinking milk supplied by the Whittier Farms Dairy.  Stephen Smith, the story’s author, wrote about this most recent death and about the illness of a pregnant woman and her baby:

milk-listeria-outbreakThe 87-year-old man fell ill in November and died Thursday, said Donna Rheaume, spokeswoman for the state department of public health.

The number of people sickened by listeria bacteria also rose to five after health officials linked a 31-year-old woman’s listeriosis, diagnosed in September, to products from the diary.

The infection was detected while the woman was in the hospital to deliver a baby, and "both mother and child are doing well," Rheaume said.

Elderly populations and pregnant women are the most vulnerable populations to Listeriosis, the illness caused by the ingestion of Listeria monocytogenes bacteria. 

Certain groups of individuals are at great risk for listeriosis. These are pregnant women (and their unborn children) and immunocompromised persons (e.g., transplant recipients). Among infants, listeriosis occurs when the infection is transmitted from the mother, either through the placenta or during the birthing process. These host factors, along with the amount of bacteria ingested and the virulence of the strain, determine the risk of disease.

Listeria can invade the body through a normal and intact gastrointestinal tract. Once in the body Listeria bacteria can travel through the blood stream, but are often found inside cells (they are "intracellular" pathogens). Listeria can co-opt the cell’s machinery to its own advantage by manipulating the host cell genes, and then move directly from cell-to-cell, avoiding many of the host’s defense mechanisms5. The bacteria also produce toxins that damages cells.

For unknown reasons, in immune-deficient hosts Listeria invades and grows best in the central nervous system, causing meningitis and/or encephalitis (brain infection). In pregnant women, the fetus is most heavily infected, leading to spontaneous abortion, stillbirths, or sepsis in infancy.