Month: November 2021

Who should get tested after a holiday indoor gathering with family members?

FA Manian MD, MPH, , , , , , , , , , , , Leave a comment

Whether you should get tested after holiday gatherings depends a lot on factors such as the level of transmission of Covid-19 within your region, the vaccination status of all the attendees, the likelihood of Covid-19 in any of the attendees, and your threshold for risk of either contracting or transmitting of Covid-19 to others, particularly immunocompromised persons. 

The following discussion assumes a scenario that is common to most indoor holiday gatherings: 1. You are getting together with people outside of your household; 2.  You or your family members don’t wear a face mask at all or certainly not all the time during the gathering; and 3. You find it impossible or don’t wish to socially distance from others during the get-together.1,2

First, let’s start with 2 situations where you should get tested following a holiday get-together, irrespective of your (or the attendees’) vaccination status: 1. if you have symptoms of Covid-19; and 2. If you were in close contact of an infected person (ie, commonly defined as within 6 feet of that person for a minimum of 15 minute during a 24-hour period).3

In the absence of known exposure or symptoms, you should consider getting tested if you are not fully immunized since you will be at higher risk of contracting and transmitting Covid-19 to others as long as there is still significant Covid-19 transmission in the region.  In contrast, if you and other attendees are fully immunized already, routine testing for Covid-19 after the gathering is hard to justify given the effectiveness of FDA-authorized Covid-19 vaccines and the costs and impracticalities associated with routine testing of millions of fully vaccinated persons.  

It goes without saying that holiday gatherings with family members outside of one’s immediate houseshold is not a zero-risk proposition for contracting or transmitting Covid-19 because people can have no symptoms and be infectious and vaccinated individuals can on occasion become infected.   Even the tests are not perfect. However, if you are concerned that you might have been exposed to Covid-19  and knowledge of a negative Covid-19 test (with its inherent limitations) gives you peace of mind, you should consider getting tested. The over-the-counter rapid Covid-19 tests may be particularly useful in assessing the likelihood of being contagious.4

For further recommendations on when you should consider getting tested for Covid-19 in general, I highly recommend an NIH-sponsored online calculator called “When to Test”.  This calculator is based on mathematical modelling that takes into account an individual’s vaccination status, transmission rates in the geographic area, and mitigation behaviors (eg, masks and social distancing).1

Bonus Pearl: Did you know that persons with Covid-19 are considered infectious 2 days before they develop symptoms or 2 days before the date of their positive test if they don’t have symptoms?5

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References:

  1. When to test offers free online tool to help individuals make informed Covid-19 testing decisions. https://www.nih.gov/news-events/news-releases/when-test-offers-free-online-tool-help-individuals-make-informed-covid-19-testing-decisions. Accessed November 26, 2021.
  2. Covid-19 testing overview. https://www.cdc.gov/coronavirus/2019-ncov/symptoms-testing/testing.html. Accessed November 26, 2021.
  3. Covid-19. https://www.cdc.gov/coronavirus/2019-ncov/php/contact-tracing/contact-tracing-plan/appendix.html#contact. Accessed November 26, 2021.
  4. Schuit E, Venekamp RP, Pas SD, et al. Diagnostic accuracy of rapid antigen tests in asymptomatic and presymptomatic close contacts of individuals with confirmed SARS-CoV-2 infection: cross sectional study. BMJ 2021;374:n1676.  https://www.bmj.com/content/374/bmj.n1676
  5. Quarantine and isolation. https://www.cdc.gov/coronavirus/2019-ncov/your-health/quarantine-isolation.html#:~:text=Get%20tested%205%2D7%20days%20after%20their%20first%20exposure.,the%20person%20with%20COVID%2D19. Accessed November 26, 2021.

Disclosures: The listed questions and answers are solely the responsibility of the author and do not necessarily represent the official views of Mercy Hospital-St. Louis, Massachusetts General Hospital, Harvard Catalyst, Harvard University, their affiliate academic healthcare centers, or its contributors. Although every effort has been made to provide accurate information, the author is far from being perfect. The reader is urged to verify the content of the material with other sources as deemed appropriate and exercise clinical judgment in the interpretation and application of the information provided herein. No responsibility for an adverse outcome or guarantees for a favorable clinical result is assumed by the author. Thank you!

 

Who should get tested after a holiday indoor gathering with family members?

What’s the evidence that a third dose of mRNA Covid-19 vaccine reduces risk of Covid-19 disease?

FA Manian MD, MPH, , , , , , , , Leave a comment

The strongest evidence to date demonstrating the effectiveness of a third dose of mRNA Covid-19 vaccine comes from an observational study from Israel which reported 93% effectiveness for admission to hospital, 92% for severe disease and 81% for Covid-19 related deaths when compared to those who had received 2 doses of the vaccine (Pfizer, BNT162b2 mRNA) at least 5 months before.1

This was a large population-based study involving over a million people 16 years or older (one-half in each group) who were eligible for the third dose (median age 52 y); those living in long-term facilities, healthcare workers and those medically confined to their homes were excluded. Vaccine effectiveness was evaluated at least 7 days after receipt of the third dose.  Median follow-up period was 13 days for both groups.

Overall effectiveness of the third dose vs 2 vaccine doses was 93% (88-97) for admission to hospital, 92% (82-97) for severe disease and 81% for death (59-97). Effectiveness of the third dose was similar between males and females and between individuals 40-60 years and those at least 70 years of age; effectiveness could not be determined in the younger age group due to small number of adverse outcomes.

What makes this study stand out among the previous works2,3 is that it controlled for important possible confounders, including sociodemographic factors, clinical factors, and behavioral factors related to Covid-19.  Limitations include its observational nature and exclusion of certain at risk groups, such as nursing home residents and healthcare workers.

Given the increasing number of Covid-19 cases in many communities at this writing, the news that a booster shot of an mRNA vaccine provides further protection in preventing Covid-19 is very welcome!

Bonus Pearl: Did you know that in a study measuring the immune response after the third dose of an mRNA vaccine (Moderna) in those 60 years of age or older, the median antibody titer rose 50-fold!4

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References

  1. Barda N, Dagan N, Cohen C, et al. Effectiveness of a third dose of the BNT162b2 mRNA Covid-19 vaccine for preventing severe outcomes in Israel: an observational study. Lancet, published online October 29, 2021. https://www.thelancet.com/action/showPdf?pii=S0140-6736%2821%2902249-2
  2. Bar-On YM, Goldberg Y, Mandel M, et al. Protection of BNT162b2 vaccine.N Engl J Med 2021; published online Sept 15, https://doi.org/10.1056/nejmoa21114255.
  3. Patalon T, Gazit S, Pitzer VE, et al. Short term reduction in the odds of testing positive for SARS-CoV-2; a comparison between two doses and three doses of the BNT162b2 vaccine. medRxive 2021;published online Aug 31. https://doi.org/10.1101/2021.008.29.21262792 (preprint).
  4.  Eliakim-Raz N, Liebovici-Weisman Y, Stemmer A, et al. Antibody titers before and aftera third dose of SARS-CoV-2 BNT162b2 vaccine in adults ages ≥60 years. JAMA. Published online November 5, 2021. doi:10.1001/jama.2021.19885 https://jamanetwork.com/journals/jama/fullarticle/2786096

Disclosures: The listed questions and answers are solely the responsibility of the author and do not necessarily represent the official views of Mercy Hospital-St. Louis, Massachusetts General Hospital, Harvard Catalyst, Harvard University, their affiliate academic healthcare centers, or its contributors. Although every effort has been made to provide accurate information, the author is far from being perfect. The reader is urged to verify the content of the material with other sources as deemed appropriate and exercise clinical judgment in the interpretation and application of the information provided herein. No responsibility for an adverse outcome or guarantees for a favorable clinical result is assumed by the author. Thank you!

What’s the evidence that a third dose of mRNA Covid-19 vaccine reduces risk of Covid-19 disease?

Why doesn’t my patient with lactic acidosis have hyperkalemia?

FA Manian MD, MPH, , , , , , , , , , , , , , , , , Leave a comment

Although hyperkalemia may be observed in a variety of conditions associated with metabolic acidosis, it is less likely to be seen in conditions associated with excess organic acids (eg, in lactic acidosis or diabetic ketoacidosis). A likely explanation for this finding revolves around the amazing organic anion transporter (OAT) and its attendant role in counteracting hyperkalemia by bringing potassium (K+) back into the cells.1-5 See details of impact of extracellular and intracellular pH on K+ homeostasis in Figure.1 

Recall that in metabolic acidosis the increased concentration of hydrogen ion (H+) outside the cell reduces sodium (Na+) influx into cells through the Na+-H+ exchange channel resulting in a drop in the intracellular Na+.  Since the Na+K+ATPase ion channel depends on the intracellular Na+ for bringing K+ into the cells, the end-result is higher K+ concentrations in the extracellular space, potentially resulting in hyperkalemia.  This is what is often seen in conditions of mineral (non-organic) acid excess (eg, in respiratory acidosis or poor renal function).

In the case of organic acidosis, however, the OAT also plays an important factor in K+ homeostasis (Figure)1.  As the name suggests, this transporter allows  organic acids such as lactic acid or ketones to enter the cell. As the H+ concentration increases intracellularly, there is more Na+-H+ exchange and more influx of Na+ into the cell.  More available Na+ intracellularly means more Na+ is pumped out by Na+K+ATPase, and more K+ is brought into the cell,1-5 mitigating the impact of metabolic acidosis on K+ efflux into the  extracellular space and potentially even causing hypokalemia! 

Concurrent hyperkalemia and lactic acidosis or diabetic ketoacidosis may of course still occur.  However, in such cases, hyperkalemia is often due to an epiphenomenon related to complicating factors.  In the case of lactic acidosis, this may be related to concurrent renal dysfunction,3 while in diabetic ketoacidosis it may be related to hyperosmolarity or insulin deficiency.1

So next time you see a patient who has hyperkalemia and lactic acidosis, ask yourself  “What else am I missing that can explain the hyperkalemia?“.

Bonus Pearl

Did you know that lactic acid in human blood was first discovered by the German physician–chemist, Johann Joseph Sherer, who sampled post-mortem blood from 2 women who died of puerperal fever in 1843? 6

Contributed by Nabi Chaudhri-Martinez MD, Mercy Hospital-St. Louis, St. Louis, Missouri

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References:

  1. Aronson PS, Giebisch G. Effects of pH on potassium: new explanations for old observations. J Am Soc Nephrol. 2011 Nov;22(11):1981-9. doi: 10.1681/ASN.2011040414. Epub 2011 Oct 6. PMID: 21980112; PMCID: PMC3231780. https://jasn.asnjournals.org/content/22/11/1981.long
  2. Orringer CE, Eustace JC, Wunsch CD, Gardner LB. Natural history of lactic acidosis after grand-mal seizures. A model for the study of an anion-gap acidosis not associated with hyperkalemia. N Engl J Med. 1977 Oct 13;297(15):796-9. doi: 10.1056/NEJM197710132971502. PMID: 19702. https://www.nejm.org/doi/10.1056/NEJM197710132971502?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub%20%200pubmed
  3. Fulop M. Serum potassium in lactic acidosis and ketoacidosis. N Engl J Med. 1979 May 10;300(19):1087-9. doi: 10.1056/NEJM197905103001905. PMID: 34793. https://www.nejm.org/doi/10.1056/NEJM197905103001905?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub 0pubmed
  4. Adrogué HJ, Madias NE. Changes in plasma potassium concentration during acute acid-base disturbances. Am J Med. 1981 Sep;71(3):456-67. doi: 10.1016/0002-9343(81)90182-0. PMID: 7025622. https://www.amjmed.com/article/0002-9343(81)90182-0/pdf
  5. Nigam SK, Bush KT, Martovetsky G, et al. The organic anion transporter (OAT) family: A systems biology perspective. Physiol Rev 2015;95:83:123. The Organic Anion Transporter (OAT) Family: A Systems Biology Perspective (physiology.org)
  6. Kompanje EJ, Jansen TC, van der Hoven B, Bakker J. The first demonstration of lactic acid in human blood in shock by Johann Joseph Scherer (1814-1869) in January 1843. Intensive Care Med. 2007;33(11):1967-1971. doi:10.1007/s00134-007-0788-7 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2040486/

Disclosures: The listed questions and answers are solely the responsibility of the author and do not necessarily represent the official views of Mercy Hospital-St. Louis, Massachusetts General Hospital, Harvard Catalyst, Harvard University, their affiliate academic healthcare centers, or its contributors. Although every effort has been made to provide accurate information, the author is far from being perfect. The reader is urged to verify the content of the material with other sources as deemed appropriate and exercise clinical judgment in the interpretation and application of the information provided herein. No responsibility for an adverse outcome or guarantees for a favorable clinical result is assumed by the author. Thank you!

Why doesn’t my patient with lactic acidosis have hyperkalemia?