News Scan for Jul 27, 2018

Top US food outbreak culprits
Salad Cyclospora total nears 300
Infectious Zika in semen

US data show norovirus, Salmonella top list of foodborne pathogens

Norovirus and Salmonella cause the most outbreaks and illnesses in food outbreaks in the United States, but Listeria, Salmonella, and Shiga toxin–producing Escherichia coli (STEC) lead to the most serious illnesses and deaths, according to Centers for Disease Control and Prevention (CDC) scientists reporting in Morbidity and Mortality Weekly Report (MMWR).

The report also notes that, when ranked by food type, tainted chicken, pork, and vegetables cause the most illnesses. The report includes data from the Foodborne Disease Outbreak Surveillance System reported to the CDC on outbreaks from 2009 through 2015.

During those years, officials reported 5,760 foodborne disease outbreaks that resulted in 100,939 illnesses, 5,699 hospitalizations, and 145 deaths. Among 2,953 outbreaks with a single confirmed source, norovirus was the most common cause (1,130 outbreaks [38%]) and produced the most illnesses (27,623 [41%]), followed by Salmonella, with 896 outbreaks (30%) and 23,662 illnesses (35%). Outbreaks involving Listeria, Salmonella, and STEC, however, were responsible for 82% of all hospitalizations and 82% of deaths reported.

Among 1,281 outbreaks involving a single food, the categories responsible for the most outbreak-related illnesses were chicken (3,114 illnesses [12%]), pork (2,670 [10%]), and what the CDC calls "seeded vegetables" (2,572 [10%]). Fish were the most commonly implicated category (222 outbreaks [17%]), followed by dairy (136 [11%]) and chicken (123 [10%]). Multistate outbreaks constituted only 3% of all outbreaks but accounted for 11% of illnesses, 34% of hospitalizations, and 54% of deaths.

Among outbreaks reporting a single location of food preparation, restaurants were the most common (2,880 outbreaks [61%]), followed by catering or banquet facilities (636 [14%]) and private homes (561 [12%]).

The authors conclude, "The causes of foodborne illness should continue to be tracked and analyzed to inform disease prevention policies and initiatives. Strengthening the capacity of state and local health departments to investigate and report outbreaks will assist with these efforts through identification of the foods, etiologies, and settings linked to these outbreaks."
Jul 27 MMWR report


Cyclospora outbreak tied to McDonald's salads expands to 15 states

The CDC yesterday reported 123 more cases in a Cyclospora outbreak linked to McDonald's salads and said 5 more states have reported related illnesses. Its update lifts the overall number of infections to 286 from 15 states.

Hardest-hit states include Illinois, which has 123 cases, Iowa (80), and Missouri (30).

However, the CDC notes that people who are part of the outbreak from Connecticut, Michigan, Tennessee, and Virginia bought salads in Illinois, and a patient from Florida had purchased a salad while traveling in Kentucky.

The most recent illness-onset date is Jul 12. Eleven people have been hospitalized, and no deaths have been reported.

McDonald's is cooperating with the investigation and has stopped selling salads at 3,000 locations in 14 states. The Food and Drug Administration (FDA) is working with McDonald's to identify common ingredients in the salads eaten by those who got sick and to trace back the ingredients though the supply chain to identify a common source. So far there's no indication that the outbreak is related to a recent Cyclospora outbreak involving Del Monte vegetable trays.

In other Cyclospora developments, Texas this week reported 29 more cases in its outbreak, according to a Jul 23 update from the Texas Department of State Health Services (TDSHS). Illnesses have been reported in 33 counties, though most patients are from Bexar, Harris, and Travis counties. Investigators are trying to determine if there's a common source for the Texas cases.
Jul 26 CDC outbreak update
Jul 26 FDA update
Jul 23 TDSHS update


Study: Infectious Zika persists in semen up to 38 days after symptom onset

CDC researchers who are studying the persistence of Zika virus in the body fluids of people who were sick in Puerto Rico's outbreak found infectious virus in semen up to 38 days after symptom onset.

In the early months of the outbreak, scientists used viral RNA to gauge duration of Zika virus to help set interim guidelines, and most information on infectious virus in body fluid samples has come from case studies or a small number of participants. The team reported its findings today in the Journal of Infectious Diseases.

Their study, comprising 297 serum samples and 97 semen samples, included a cohort of patients in Puerto Rico who had lab-confirmed infections, and the team was also able to look for infectious virus in blood and compare their finding from both body fluids with Zika viral RNA in the same specimens. They assessed infectious Zika virus by virus passage in Vero cell cultures.

The investigators detected Zika up to 38 days after the onset of symptoms, much shorter than the maximum of 370 days for the detection of Zika RNA in semen. The persistence they found was similar to a case study in which sexual transmission occurred 44 days after symptom onset. They found that serum viral RNA load was about 10 times lower than in semen at the time of sampling, which the team said could explain why Zika isolation rate is much lower in serum than in semen. The researchers were only to isolate Zika virus from blood only at 3 days after symptom onset.

They concluded that the study adds more insights into persistence of Zika in semen and blood, and the duration they found in semen is well within the CDC's recommendation for abstaining from sex or using condoms for 6 months after illness to avoid sexual transmission.

A meta-analysis published earlier this week found that the maximum duration of sexual transmission after symptom onset was 44 days.
Jul 27 J Infect Dis abstract
Jul 24 CIDRAP News story "Study suggests smaller window for Zika sexual transmission"

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