Asymptomatic COVID-19 may not spread as easily as symptomatic
Symptomatic COVID-19 cases are responsible for more viral transmission than asymptomatic infections, suggests an updated systematic review and meta-analysis of 130 studies published yesterday in PLOS Medicine.
A team led by University of Bern researchers in Switzerland searched databases through Jul 6, 2021, for studies on COVID-19 patients with documented symptom status at the start and end of follow-up, as well as mathematical modeling studies. The studies included data on 28,426 COVID-19 patients from 42 countries, 11,923 (42%) of whom were asymptomatic.
Because heterogeneity among the studies was high, the team didn't estimate the average proportion of asymptomatic cases overall or in 84 screening studies of defined populations.
In 46 contact-tracing or outbreak studies, the total share of asymptomatic COVID-19 cases was 19% (95% confidence interval [CI], 15% to 25%; prediction interval [PI], 2% to 70%). Relative to symptomatic infections, the rate of viral spread from asymptomatic index patients to contacts was about two-thirds lower (risk ratio, 0.32; 95% CI, 0.16 to 0.64; PI, 0.11 to 0.95; 8 studies). Thirteen modeling studies fit to data revealed that the proportion of all viral transmission from presymptomatic patients was higher than that of those who were asymptomatic.
"When SARS-CoV-2 community transmission levels are high, physical distancing measures and mask-wearing need to be sustained to prevent transmission from close contact with people with asymptomatic and presymptomatic infection," the researchers wrote.
But they cautioned that the study was limited by high heterogeneity and high risks of selection and information bias in studies not designed to quantify persistently asymptomatic cases, as well as limited data about SARS-CoV-2 variants in vaccinated participants.
"The true proportion of asymptomatic SARS-CoV-2 infection is still not known, and it would be misleading to rely on a single number because the 130 studies that we reviewed were so different," senior author Nicola Low, MD, of the University of Bern, said in a PLOS Medicine news release. "People with truly asymptomatic infection are, however, less infectious than those with symptomatic infection."
May 26 PLOS Med study and news release
Salmonella outbreak tied to peanut butter grows as more foods recalled
The US Centers for Disease Control and Prevention (CDC) yesterday reported 2 more Salmonella Senftenberg cases in an outbreak linked to peanut butter, raising the national total to 16 people from 12 states.
The latest illness onset is May 2, and, of people with available information, two have been hospitalized. No deaths have been reported. The CDC said the true number of people infected is likely much higher, given that most people recover without needing care and because of the delay in confirming that illnesses are part of an outbreak.
Interviews with sick patients revealed that most had eaten Jif brand peanut butter, and on May 20, J.M. Smucker, which makes Jif, recalled Jif types of peanut butter. Also, 13 companies have recalled their products such as candy and prepackaged snack trays that contain servings of the recalled Jif peanut butter.
May 26 CDC outbreak update
May 20 FDA Jif peanut butter recall announcement
FDA list of related recalls
Pakistan reports 3 more wild polio cases
In its latest weekly update, the Global Polio Eradication Initiative (GPEI) said Pakistan reported its third wild poliovirus type 1 (WPV1) case of the year, in a patient from Khyber Pakhtunkhwa, which was followed by news today from Pakistani media of two more WPV1 cases.
The two cases confirmed today by the Pakistan National Polio Lab include two children in the same family, a girl who had a May 10 paralysis onset and a boy who had a May 11 paralysis onset, according to Pakistan Today. The report said the country has six WPV1 cases this year.
Pakistan and Afghanistan are the two countries where WPV1 is still endemic, and the uptick in cases this year is a discouraging development, as it followed a steep downturn in cases over the past few years.
In other polio developments, four countries reported more circulating vaccine-derived poliovirus type 2 (cVDPV2) cases, GPEI said in its update. Chad reported two cases, one in Batha department and the other in N'Djamena, the nation's capital, raising its total to three this year. The Democratic Republic of the Congo (DRC) reported 10 more cases, mostly in Maniema province, raising its total for 2022 to 47.
Elsewhere, Niger reported one more case, which involves a patient from Tillaberi and brings its total for the year to two. And Yemen reported 12 more cases in nine locations, boosting its 2022 total to 17.
May 26 GPEI update
May 27 Pakistan Today story
USDA announces $400 million more for avian flu response
For the third time, US Department of Agriculture (USDA) Secretary Tom Vilsack has approved funding to help the agency and its state and local partners quickly identify and manage ongoing highly pathogenic avian flu outbreaks in poultry.
In an announcement today, the USDA said it approved the transfer of $400 million from the Commodity Credit Corporation (CCC) to fund the outbreak response. The move follows a $130 million transfer in March and a $263 million transfer in late April. The CCC was established in the 1930s to stabilize, support, and protect farm income and prices.
Since the transfer in late April, there have been 151 more detections in poultry, including flocks in nine newly affected states, which led to the loss of 10.8 commercial and backyard birds.
May 27 USDA announcement
In other outbreak developments, the USDA's Animal and Plant Health Inspection Service (APHIS) reported one more outbreak in poultry, which involved a backyard flock in King County, Washington, near Seattle.
Also, APHIS reported 105 more detections in wild birds, bringing the total to 1,295. Most of the detections were in Wisconsin, Minnesota, and North Dakota, but several were from western states such as Alaska, Utah, Wyoming, Idaho, and Montana. There was one in the East, in New York. Most new detections were in raptors found dead. There were a few in other types of birds, including gulls, crows, and waterfowl.
USDA APHIS poultry avian flu page
USDA APHIS wild bird avian flu page
UK reports more unexplained hepatitis cases in kids
The United Kingdom today reported 25 more unexplained hepatitis case in kids, raising its total to 222, according to an update from the Health Security Agency (HSA), and the World Health Organization (WHO) says it is tracking 650 probable cases.
So far, most of the cases are in kids younger than 5, but the HSA said a small number of children who are older than 10 are part of the investigation.
Renu Bindra, MD, senior medical advisor and incident director, said in a statement, "Our investigations continue to suggest an association with adenovirus, and we are exploring this link, along with other possible contributing factors including prior infections such as COVID-19."
In April, the country was the first to sound the alarm about unexplained hepatitis cases in children. Since then, more than 600 cases, 14 of them fatal, have been reported by more than 30 countries.
May 27 UK HSA update
In an update today, the WHO says 33 countries in five WHO regions have reported 650 probable cases total, with an additional 99 cases pending classification.
Of the 650 cases, 374 (58%) have been in the WHO European Region, with the Americas reporting 240 cases (37%), far outpacing the Western Pacific (34 cases), Southeast Asia (14), and the Eastern Mediterranean (5). The WHO reported the same number of UK cases as did the HSA (222), adding that the United States has had 216.
May 27 WHO update
