Dysfunction of smell, taste post-COVID-19: will they persist? | Latest news for doctors, nurses and pharmacists

Ofactorial and taste losses/alterations** are common symptoms of COVID-19, but recovery is expected in most patients within the first 3 months.
However, these dysfunctions may persist in some individuals, according to a
reconstructed meta-analysis of Singapore.

“[P]persistent smell and taste dysfunction could be considered a focal neurological deficit and may impact quality of life and general health long after recovery from COVID-19,” the researchers said. “Given the potentially serious sequelae associated with [these] dysfunctions, and the need for physicians to counsel patients on their anticipated recovery journey, it is essential to investigate the burden of persistent symptoms and identify relevant prognostic factors.

In this meta-analysis (n=3,699 [18 studies]), three-quarters of participants recovered their sense of smell (74%) and taste (79%) at 30 days. These continued to improve at day 180, almost all recovered (96% [smell] and 98 percent [taste]). [BMJ 2022;378:e069503]

Based on parametric modeling of healing, persistent self-reported smell and taste dysfunction could develop in approximately 5.6% and 4.4% of patients with initial dysfunction, respectively. [BMJ 2022;378:o1939]

These numbers may seem nominal, but given that more than half a billion people worldwide contracted COVID-19 in July 2022, these estimates translate to more than 15 million people with ongoing olfactory dysfunction, while that more than 12 million people have been left with a persistent taste disorder. [ACS Chem Neurosci
2020;11:2944-2961] “This result could contribute to the growing burden of long COVID,” they said.

Additionally, self-reporting may have overestimated recovery, implying that the true burden of olfactory dysfunction may be even greater. [BMJ 2022;378:o1895]

Underlying mechanisms

The delayed odor recovery can be attributed to the varying rates at which support cells and sensory neurons regenerate due to varying degrees of inflammation, the researchers noted. “Stem cell damage and severe inflammation may also prolong smell dysfunction by slowing olfactory regeneration. [epithelium].”

For delayed taste recovery, binding of SARS-CoV-2 to ACE2** receptors in the salivary glands can impair salivary flow, triggering “conductive” taste dysfunction. [Int J Oral Sci
2020;12:8] “Viral binding to cells in the oral mucosa could trigger inflammation, abnormal cell turnover, and reduced taste bud sensitivity and thus neurosensory taste dysfunction, which may have variable regeneration rates,” they said.

Poorer recovery in women

Recovery of these senses was also less likely in women than in men (odds ratio [OR]0.52 [smell] and OR, 0.31 [taste]). “One reason could be the better basic olfaction and taste in [women]which may result in greater sensitivity to change and greater subjective impairment,” the researchers said.

Another possible mechanism is the upregulation of ACE2 expression by estrogen. [Biol Sex Differ
2020;11:29] “[T]The ACE2 receptor…may have higher expression in females, or may express heterodimers that alter virus binding, thereby potentially increasing viral invasion in females,” they added.

Unanswered questions

Further studies are warranted to shed light on why women are particularly affected and to determine if there are any methods patients can use to speed recovery. It remains to be determined if the sensory loss would be permanent or if olfactory training could improve the results.

“These are important questions…that need to be taken seriously and investigated by the medical and research community,” the researchers stressed.

“Even as we learn to live in the age of the COVID-19 pandemic, we must keep in mind that COVID-19 is not just a simple cough and cold, but can have far-reaching consequences and sustainable,” they said. said. “Persistent loss of smell and taste is just one of many health issues across the long COVID disease spectrum, and it remains clear that more can and should be done for these patients.”

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