Higher viral load associated with COVID-19 transmission risk
Higher viral loads of SARS-CoV-2, the virus that causes COVID-19, are associated with an increased risk of transmission, according to cohort study results from Catalonia, Spain, published yesterday in The Lancet Infectious Diseases,
Researchers found that the overall secondary attack rate was 16.6%, although they ranged from 12% when the index case had a viral load lower than 1·106 copies per milliliter (mL) to 24% when viral load was 1·1010 copies per mL or higher.
Viral loads are not a set value, but previous research has shown they peak around the time of symptom onset, notes a related commentary by Laura Cornelissen, MD, and Emmanuel André, MD, PhD, two Belgian infectious disease experts.
Ninety of the 282 index cases (31.9%) in the study had at least one transmission event. Secondary attack rates Of the transmission events, 90% occurred in clusters where the index case had a viral load of 5.1 log10 copies per mL or higher and 50% had a viral load of 8.8 log10 copies per mL or higher.
The researchers used the same population as a previous hydroxychloroquine COVID study, drawing viral loads and infection timelines from 282 non-hospitalized adults positive with COVID-19. Each adult had at least one close contact from Mar 17 to Apr 28, 2020. Increased risk was associated with household contacts (odds ratio [OR], 3.0; 95% confidence interval [CI], 1.59 to 5.65) and contact age (per-year OR, 1.02; 95% CI, 1.01 to 1.04).
Duration between exposure and symptom onset was inversely associated with the index case's viral load, going from 7 days when infected by an initial viral load lower than 1 X 107 copies per mL to 5 days when the initial viral load was 1 X 109 copies per mL or higher. The index case's age, sex, respiratory symptoms (eg, coughing), and mask usage were not associated with risk transmission.
"Rather than questioning the usefulness of mask-wearing policies, these results underscore the necessity of a multi-layered comprehensive approach to infection prevention and control," Cornelissen and André write. They also expand on the researchers' idea of using viral load as a means for risk stratification, saying that to do so would necessitate polymerase chain reaction tests that are not only quantitative but also standardized.
Feb 2 Lancet Infect Dis study
Feb 2 Lancet Infect Dis commentary
Strict mitigations may have minimized COVID cases at YMCA camps
Out of 6,830 youth and staff, 19 primary COVID-19 infections (0.6%) were linked to 2 secondary infections (0.07% of 3,030 contacts) at 54 YMCA day camps over several months, reports a study today in Pediatrics.
While other summer camps have reported high transmission rates, the researchers say the YMCA's mitigations—and staff and youth adherence to them—may have helped keep COVID-19 attack rates low.
The YMCA camps were hosted across six counties in North Carolina over 133 days from March to August 2020. Mitigations included daily temperature checks, frequent hand washing, staff training, site cleaning, and mask usage indoors and whenever physical distancing wasn't possible (which, according to an internal June audit, was adhered to more than 95% of the time).
Cohorts were also used, with the average size being 20 youth and 6 staff across 5 days. Of those who got sick, 55% had fevers and 45% had coughs; hospitalization was not required.
The average age of youth and staff were 8.5 and 22 years, respectively.
While the researchers acknowledge the possibility of under-reported or undetected cases, their findings indicate that most primary cases were most likely products of community or household transmission.
"Although minority youth were more likely to attend indoor camps (where expected transmission risks may be increased)," they add, "we did not observe higher transmission rates in these settings. This finding may be particularly relevant to school and other congregate care settings where the majority of time has to be spent indoors due to weather or learning conditions."
Feb 3 Pediatrics study
Source unknown in E coli outbreak linked infections in 5 states
The US Centers for Disease Control and Prevention (CDC) said yesterday that an investigation is under way into the source of an Escherichia coli O157:H7 outbreak that has so far sickened 16 people in five states, 1 of them fatally.
Affected states are Washington, Oklahoma, Arkansas, Virginia, and New York. The first illness was reported on Dec 23, and the most recent symptom onset was Jan 7. Patient ages range from 10 to 95 years, and 88% are female.
Of 12 patients with available information, 9 were hospitalized. And of 11 people with more detailed status, 3 had hemolytic uremic syndrome, a potentially fatal kidney complication. The person who died was from Washington.
State and local health officials are interviewing people to see what they ate the week before they got sick. Health officials are using PulseNet, the national subtyping network, to find other illnesses that might be part of the outbreak.
Whole-genome sequencing suggests the E coli from sick people is closely related and that they were probably sickened by the same type of food. Sequencing also suggests that the outbreak strain has been linked in the past to a variety of sources, including romaine lettuce, ground beef, and recreational water.
Feb 2 CDC outbreak notice
