2018 E. coli outbreaks: Timeline of an illness

The Centers for Disease Control and Prevention (CDC) reports that it investigated three 2018 E. coli outbreaks, two from contaminated romaine lettuce and the other from contaminated ground beef.

On its home page for E. coli, the organization links to a page that outlines the process of investigating an E. coli outbreak, “Timeline for Reporting Cases of E. coli O157 Infection.” Here is that process:

2018 E. coli outbreaks:
taking DNA fingerprints

E. coli O157 – or Escherichia coli O157 – is the most commonly identified serotype of Shiga-toxin producing E. coli (STEC) bacteria. (The testing done to distinguish E. coli O157 from its counterparts is called “serotyping.”)

To determine the serotype of STEC, public health laboratories perform a kind of “DNA fingerprinting” on lab samples. Investigators determine whether the DNA pattern of E. coli O157 bacteria from one person is the same as that from others sickened in an outbreak as well as bacteria taken from the contaminated food, water, or animal.

Bacteria with the same “DNA fingerprint” are likely to come from the same source. Public health officials will then conduct an investigation, including interviews with those sickened, to determine if they are part of a common-source outbreak.

2018 E. coli outbreaks:
illness timeline

A series of events occurs between when a person is infected and the time officials can determine they are part of an outbreak. This produces a delay between when a person gets sick and confirmation that they are part of an outbreak.

Officials work hard to speed up the process. The timeline is as follows:

Time to illness

This is the time from when a person is exposed to E. coli O157 to the beginning of symptoms (also called the “incubation period”). For E. coli O157, this is usually one to three days.

Time to contact with doctor

The time from the first symptom until the person sees their doctor, when a stool sample is collected for laboratory testing. This is usually one to five days.

Time to diagnosis

The time from when a person gives a stool sample to when E. coli O157 is detected from the sample in a laboratory. This can take up to three days from the time the sample is received by the lab technician. The diagnosis of E. coli infection can be reported to the local health department at this time.

E. coli transfer time

The time required to ship the E. coli O157 bacteria sample from the laboratory to the public health authorities who will perform “DNA fingerprinting.” This can take up to a week, depending on transportation arrangements within a state and the distance between the laboratory and public health department.

Time to “DNA fingerprinting”

The time required for the state’s public health authorities to perform “DNA fingerprinting” on the E. coli O157 isolate and compare it with the pattern of the outbreak strain. This can be accomplished in one day, but because many public laboratories have limited staff and space and experience numerous emergencies simultaneously, it can take up to four days.

Add it all up, and the time from the beginning of a person’s illness to the confirmation that the illness is part of an outbreak is about two to three weeks. That’s why case counts during an outbreak investigation are considered “preliminary” and almost inevitably increase over time.

2018 E. coli outbreaks:
romaine, ground beef

The STEC that caused both romaine lettuce outbreaks was – not surprisingly – E. coli O157. In the ground beef outbreak, however, the STEC was E. coli O26.

In addition to E. coli O157, many other kinds (called serogroups) of STEC cause disease. Other E. coli serogroups in the STEC group, including E. coli O26, are sometimes called “non-O157 STECs.” There are limited public health data on the occurrence of non-O157 STECs.

Compared with STEC O157 infections, identification of non-O157 STEC infections is more complex. First, laboratories must test stool samples for the presence of Shiga toxins. Then, the positive samples must be sent to public health laboratories to look for non-O157 STEC. (Clinical laboratories typically cannot identify non-O157 STEC.)

In addition to O26, other non-O157 STEC serogroups that often cause illness in the United States include O111 and O103. Some types of STEC frequently cause severe disease, including bloody diarrhea and hemolytic uremic syndrome (HUS), which is a type of kidney failure.

2018 E. coli outbreaks:
illness symptoms

Anyone can become sick by eating food or drinking water contaminated with E. coli, but people with the highest risk of developing HUS include the very young and the very old, as well as anyone with a weakened immune system, especially pregnant women.

Symptoms of an E. coli illness are similar to those of other types of food poisoning: