A Listeria monocytogenes outbreak that has hospitalized 10 people in two states has now been linked to ready-to-eat food from California-based Fresh & Ready foods that were served at the institutions, the US Food and Drug Administration (FDA) and Centers for Disease Control and Prevention (CDC) said in a May 10 investigation update.

Eight cases are in California and two in Nevada, but the CDC said the true number is likely higher, because some people recover without medical care. No deaths have been reported.

The CDC said it first investigated the outbreak in 2024, which involved people who were hospitalized before they got sick, suggesting food served in the institutions was the likely source. However, there wasn't enough information to tie the illness to a specific food.

Positive environmental sample was a breakthrough clue

Officials reopened the investigation after the outbreak strain was found in environmental samples collected in late March from Fresh & Ready Foods. State and local health officials interviewed six patients about foods they ate in the month before they became ill. Trace-back records revealed that ready-to-eat foods from the company were served in at least three of the facilities.

On May 10 the company voluntarily recalled certain ready-to-eat foods, which included sandwich and snack items distributed during the last half of April for vending and break rooms in corporate offices, medical buildings, and healthcare facilities in Arizona, California, Nevada, and Washington state. They were sold under the Fresh & Ready Foods, City Point Market Fresh Food to Go, and Fresh Take Crave Away brands.

A meta-analysis of 9,600 pregnant women and newborns estimates a more than fourfold higher risk of severe microcephaly in babies born to Zika virus–infected mothers.

Zika virus is primarily spread by infected Aedes mosquitoes, unprotected sex, and transfusion with contaminated blood. Microcephaly is a rare condition in which a baby's head is smaller than normal due to abnormal brain development in utero or after birth. The condition is associated with developmental and neurologic challenges as the child grows.

In July 2018, the Zika Virus Individual Participant Data Consortium systematically searched the literature for observational longitudinal or surveillance studies on Zika virus infection during pregnancy that measured fetal, infant, or child outcomes and involved at least 10 participants.

For the main analysis, the researchers identified 18 studies composed of 24 unique datasets on 9,568 pregnant women and 9,608 newborns from 11 countries. They used variables related to pregnancy, Zika diagnostic methods, and fetal characteristics and outcomes to harmonize the data across studies with standardized definitions. A sensitivity analysis included 22 studies with 28 datasets.

The goal was to assess any link between maternal Zika infection and miscarriage, microcephaly, and congenital Zika syndrome (CZS). 

The findings were published late last week in eClinicalMedicine.

Over half of newborns had microcephaly

Five of 22 studies noted that over 50% of newborns had microcephaly, and the same number of studies observed that over 5% had CZS. In addition, 4 of 22 reported a miscarriage rate over 3%. The risk of severe microcephaly was significantly greater in Zika-positive pregnancies than in virus-negative pregnancies (1.5% vs 0.3%), with a relative risk of 4.5. 

Women of reproductive age should be informed about the risks of Zika infection during pregnancy to support reproductive planning.

"Our findings align with previously published meta-analyses and indicate an added burden to adverse pregnancy outcomes with higher prevalence compared to pre-epidemic population-based average values," the study authors wrote. "Women of reproductive age should be informed about the risks of Zika infection during pregnancy to support reproductive planning."

They called for future research on other pregnancy outcomes with clear definitions of maternal Zika infection.