By Carol A. Kemper, MD, FACP

Clinical Associate Professor of Medicine, Stanford University, Division of Infectious Diseases, Santa Clara Valley Medical Center

Risk of COVID-19 During Air Travel

SOURCE: Hu M, Wang J, Lin H, et al. Risk of SARS-CoV-2 transmission among air passengers in China. Clin Infect Dis 2021 Sept 21; ciab836.doi: 10.1093/cid/ciab836. [Online ahead of print].

Everyone wants to travel for the holidays — and there has been lots of conversation about the risk of COVID-19 transmission during air travel. Some have argued that the type of airplane might make a difference. Most, but not all, commercial jet liners are equipped with high efficiency particulate air (HEPA) filters, and about 40% of the cabin air is recirculated through this HEPA system, which can filter 99.97% of dust, pollen, bacteria, viruses, and any other airborne particles with a size of 0.3 microns or greater. Another 60% of the air is piped into the plane while cruising. Most commercial air flights completely recycle the air within the cabin every three minutes, with about 20 air exchanges per hour.

To assess the risk of COVID-19 transmission during air travel, before mask requirements and other precautionary measures, these authors examined domestic flights leaving Wuhan, China, from Jan. 4 through Jan. 22, 2020, the day before the lockdown. An index case was defined as a confirmed diagnosis of COVID-19 infection following air travel, plus symptom onset within 14 days of departure and within two days of travel, and had the earliest date of symptom onset if one or more cases within three rows of seats. Secondary COVID-19 cases were defined as symptom onset within two to 14 days of travel.

The risk of transmission during actual air flight is hard to estimate, since people may have exposures en route to the airport, within the terminal, or during exit from the plane, not to mention that many people may travel with friends, family, or coworkers, with additional risk for exposure at home or at work. In an attempt to manage these varying risks, the authors calculated both the upper and lower estimates of secondary attack rates. The upper bound was calculated assuming no work/family relationship between the case, and then they recalculated the lower bound by assuming the person seated next to an index cases was related, and excluded this individual from the estimates.

In all, 5,797 people took 177 domestic flights from Wuhan. A total of 209 travelers were confirmed with COVID-19 infection within two weeks of travel, of which 175 were considered index cases. There were 34 secondary cases, with a median of 4.0 days from departure to symptom onset. The upper bound’s secondary attack rate was 0.6% and the lower bound’s secondary attack rate was 0.33%. Each index cases resulted in 0.19 to 0.10 secondary infections, respectively (this is pre-mask requirement and pre-vaccination).

However, seat proximity and flight duration were significant factors in the risk of transmission. Seats immediately adjacent to a case had a 9.2% attack rate, with a relative risk of 27.8 compared with other seats on the airplane. The middle seat had the highest attack rate (0.7%) compared with the window and aisle seats (0.6%), most likely because middle seats have twice the chance of sitting next to someone with COVID-19 infection. The upper bound’s attack rate was 0.7% for flights less than two hours to 1.2% for flights of 2 to 3.3 hours, whereas the lower bound’s estimates of transmission for the same durations were 0% and 0.4%. No difference was observed between Airbus and Boeing jet liners.

The risk of COVID-19 transmission during air travel from Wuhan, China, before the lockdown in January 2020 was small (0% to 0.9%), depending on the duration of the flight, unless a passenger happened to sit next to an index case, in which case the risk ballooned to 9.2%. Face mask requirements and higher vaccination rates in air travelers will further reduce these estimates. Just make sure you do not sit next to someone with COVID. 


Symptoms Post-COVID: Loss of Taste in One in Seven 

SOURCE: Nehme M, Braillard O, Chappuis F, et al. Prevalence of symptoms more than seven months after diagnosis of symptomatic COVID-19 in an outpatient setting. Ann Intern Med 2021;174:1252-1260.

Persistent complaints of physical and mental debility are common in people who have been infected with COVID-19, and some patients may take months to return to work. These authors examined self-reported symptoms at 30-45 days and seven to nine months following diagnosis in a group of relatively healthy, younger adults (18 years of age or older), followed in a COVID ambulatory care clinic in Switzerland. Because COVID-19 patients were not followed in the usual ambulatory care setting, Switzerland’s Geneva General Hospital established CoviCare clinics, originally established to follow positive patients every two days by telephone during the first 10 days of their illness. They were contacted again for a telephone interview and were sent an on-line questionnaire at days 30-45 and at seven to nine months.

A total of 629 individuals participated in the prospective survey, of which 410 completed seven to nine months of follow-up. The mean age was 42.1 years, 61% were female, and 70.7% had no underlying risk factors. Twenty-five percent were healthcare workers. Most of the patients (96%) were symptomatic at baseline, and the majority reported their symptoms as mild to moderate. Despite being relatively younger and healthier, 40 participants were hospitalized during follow-up. Of the 311 patients who participated at all three time points, 37% reported symptom resolution at days 30-45 and 56% reported symptom resolution by months 7 to 9.

In all, 39% of participants reported residual symptoms at months 7 to 9, including, in descending order of frequency, fatigue (20.7%), loss of taste and/or smell (16.8%), dyspnea (11.7%), and headache (10%). Persisting mental symptoms included difficulty concentrating (5.9%), insomnia (5.7%), and memory loss (5.6%). Women were more likely than men to have persistent symptoms (43.2% vs. 31.1%) at months 7 to 9, and increasing age was associated with a greater frequency of residual symptoms.

When arguing in favor of COVID-19 vaccination, I have stressed that COVID-19 is not just an acute infection but a real disease, with prolonged symptoms for months in four of 10 people infected, even in people who are relatively young and healthy. I mention several people who now are effectively disabled and cannot work or support their families. But what impresses people the most is that one in seven may lose the sense of taste or smell — and it is not just loss of taste or smell, but food actually may taste bad. Can you imagine going through the rest of your life without enjoying food? Try this when counseling people regarding vaccination! 


Effectiveness of Cloth and Surgical Masks Against SARS-CoV-2

SOURCE: Adenaiye OO, Lai J, Bueno de Mesquita PJ, et al. Infectious SARS-CoV-2 in exhaled aerosols and efficacy of masks during early mild infection. Clin Infect Dis 2021; Sept 14:ciab797. [Online ahead of print].

Newer variants of SARS-CoV-2 are generally believed to be more transmissible. So how well do regular cloth or surgical masks work against the newer variants? These authors examined the efficacy of usual cloth masks and surgical masks in 49 non-vaccinated COVID-19-positive college students, who provided blood, saliva, mid-turbinate, and fomite (phone mouthpiece) specimens, and 30-minute breath samples with and without masks. Participants were asked to speak loudly and sing into a Gesundheit-II breath sampler for 30 minutes. Samples were collected on two or more visits at least two days apart within 0-12 days of a positive test or onset of symptoms. Participants were tested without a mask, with a surgical mask, and with the cloth mask they brought with them to the testing. Viral ribonucleic acid (RNA) was quantified, and cultures were performed on VERO cell media.

In unmasked participants, viral RNA was found in 31% of coarse droplets (> 5 µm) and 45% of fine aerosols ( 5 µm), as well as 65% of fomite samples from the telephone mouthpiece. The amount of viral RNA detected in coarse and fine aerosols was reduced by 77% and 48%, respectively, when wearing either a cloth or surgical mask; no significant difference was observed between different mask types. Quantitative RNA in mid-turbinate swabs (but not saliva) was strongly associated with the amount of virus observed in aerosols. Interestingly, virus could be cultured in 68% of mid-turbinate specimens, 32% of salivary specimens, but only 3% of the fine aerosol samples in persons wearing a mask, and none of the fine aerosol samples from persons not wearing a mask. In addition, none of the fomite samples were culture-positive.

Four of the individuals were found to have the newer alpha variant virus, whereas the others were infected with earlier strains. Viral shedding was significantly greater in these four individuals (18-fold greater). When adjusted for cough and mask wearing, viral RNA was 100-fold greater in coarse aerosols and 73-fold greater in fine aerosols, suggesting that newer strains are indeed more transmissible.

Ordinary cloth and surgical face masks provide a moderate reduction in the exhaled virus in 30-minute breath samples in COVID-19-infected, unvaccinated persons, although newer more transmissible variants were more likely to generate aerosols with greater amounts of viral RNA. Samples in this study were obtained from students who were speaking loudly and singing into a breath sampler for an extended period of time, which likely increased the risk of finding detectable RNA, but probably more closely mimics the real world, e.g., sitting around a dinner table or chatting at a bar.