Study links mode of birth, antibiotic use to more antibiotic resistance genes in infants

News brief

Baby delivered by C-section — mvaligursky / iStock

A meta-analysis of genomic data on infant gut microbiomes from 10 countries indicates that cesarean (C-section) delivery, antibiotic use, and prematurity are associated with increased gut carriage of antibiotic resistance genes (ARGs) in infants, according to a study that will be presented at the upcoming European Society of Clinical Microbiology and Infectious Diseases (ESCMID) Global Congress in Barcelona Spain.

The study, led by researchers from the Arctic University of Norway-Tromso, looked at 14 studies that included 3,981 gut metagenome fecal samples from 1,275 infants in 10 countries. Their aim was to determine gut carriage of ARGs and mobile genetic elements (MGEs) and evaluate the impact of birth mode, antibiotic use, prematurity, and feeding practices on the infant gut resistome (the collection of ARGs in the genomes of infant gut microbes) and mobilome (the collection of MGEs). Previous studies have found that antibiotic use in preterm infants is associated with reduced diversity of gut bacteria compared with healthy infants.

Reduced bacterial diversity, more resistance genes

Overall, the researchers found 199 clinically relevant ARGs, whose diversity increased with age during the first 2 years of life. When compared with full-term, vaginally born infants not exposed to antibiotics, premature infants delivered by C-section and administered antibiotics had reduced beneficial gut microbe diversity but a higher abundance of ARGs and MGEs. Formula feeding versus breastfeeding had no significant effect on ARG diversity or abundance.

Studies that included infants from South Africa and Zimbabwe found a statistically significant and higher ARG and MGE abundance compared with European infants.

The researchers also found that Enterobacterales, specifically Escherichia coli, were key contributors to ARG load.

While many gut microbes carrying ARGs don't pose a health threat, the presence of MGEs indicates the potential for sharing ARGs with pathogenic bacteria.

"This has important implications for the antibiotic resistance crisis," lead study author Ahmed Bargheet, PhD, said in an ESCMID press release. "By gaining insight into these factors, we aim to develop targeted interventions like probiotics, that could significantly reduce the number of deaths caused by antimicrobial resistance."

Impaired sense of smell still common 1 year after COVID-19

News brief

Stephanie Soucheray, MA

Sense of smell—but not taste—was still impaired in some COVID patients at 1 year, according to a new study in JAMA Network Open.

The US-based cross-sectional study compared 340 people with and 434 without prior COVID-19, recruited from February 2020 to August 2023 from the social media website Reddit.

Researchers instructed participants to take the 53-item Waterless Empirical Taste Test (WETT) and 40-item University of Pennsylvania Smell Identification Test (UPSIT) to assess taste and smell function.

Loss of taste and smell was one of the first symptoms most commonly ascribed to COVID-19 infections, but few studies have looked at the loss after 1 year, or in infections caused by newer variants. Furthermore, only a handful of studies have been based on smell and taste tests.

Participants in the study had a mean time between testing and COVID-19 diagnosis of 395 days (95% confidence interval [CI], 363 to 425 days). The total WETT scores did not differ significantly between participants with and without a COVID-19 history, with both groups falling within normal ranges.

Almost a third with prior COVID had loss of smell

The UPSIT test assessing smell, however, showed that people with COVID-19 had mean scores that were significantly lower than those without a history of COVID (age- and sex-adjusted mean, 34.4 [95% CI, 33.9 to 34.9] compared to 35.9 [95% CI, 35.4 to 36.3], a 4.2% reduction.

Participants with a history of COVID-19 were more likely to experience some degree of smell loss compared with those without a history (30.3% vs 21.0%; odds ratio [OR], 1.64; 95% confidence interval [CI], 1.18 to 2.27). Moderate to severe loss of smell was likewise higher in those with previous COVID-19 (8.5% vs 2.8%; OR, 3.28; 95% CI, 1.65 to 6.53).

Reports that taste loss continues long after the initial infection probably are due in large part to the confusion between taste- and olfaction-dependent food flavor.

"Reports that taste loss continues long after the initial infection probably are due in large part to the confusion between taste- and olfaction-dependent food flavor," the authors explained. "Smell loss remained in nearly one-third of individuals with exposure, likely explaining taste complaints of many individuals with [long COVID]."

Babies of dengue-infected pregnant women shown to be at high risk for poor health in first years of life

News brief

Mary Van Beusekom, MS

Newborn baby — *GODS_AND_KINGS / iStock*

The children of women infected with dengue virus during pregnancy are much more likely to be born at a very or extremely low birth weight, which can negatively affect their health for at least the first 3 years of life, suggests a study published in the American Economic Journal: Applied Economics.

Researchers from the University of Surrey and the University of Birmingham analyzed a large dataset on dengue-infected pregnant women and birth outcomes in southeastern Brazil.

Dengue fever is the most common mosquito-borne illness in the world. "There has been a dramatic rise in cases over recent years, with cases in the Americas reaching more than three million cases in 2023," the study authors wrote. "Since January 2024, Brazil has reported more than 3.5 million cases, marking the largest dengue outbreak on record."

67% and 133% higher risk of very, extremely low birth weight

The newborns of women who had even mild dengue fever during pregnancy had a 67% and 133% greater risk of being classified as very and extremely low birth weight, respectively. From birth to 3 years, the children were at a 27% higher risk of hospitalization, with a 76% increase in risk at 2 years.

Policy changes and things like vector control, updated risk communication with key groups and vaccine adoption can all reduce the risk of pregnant women being infected with dengue.

Livia Menezes, PhD

"These birth outcomes can even have longer-term impacts; for example, previous research has shown that low birth weight can negatively affect socio-economic outcomes and health in adulthood," coauthor Livia Menezes, PhD, of the University of Birmingham, said in a university news release.

Coauthor Martin Foureaux Koppensteiner, PhD, of the University of Surrey, said the negative birth outcomes also affect dengue-endemic communities. "Hospitalisations and ongoing health issues resulting from maternal infections all have a cost, and one that could be avoided, or at least minimised with increased awareness and improved policy," he said.

"Policy changes and things like vector control, updated risk communication with key groups and vaccine adoption can all reduce the risk of pregnant women being infected with dengue," Menezes said.