Respiratory infections are certainly one of the major reasons for medical consultation or use of emergency services, as well as hospitalization and even mortality (it is estimated that an average of 16 people die of pneumonia/respiratory infection per day in Portugal alone). Many of them are of viral origin, caused by numerous types of viruses, of which influenza (flu) and coronaviruses (and respiratory syncytial virus in children and the elderly) stand out.
They are therefore not caused by any sudden change in temperature, exposure to the cold or the sun! And most of them do not require antibiotics, given so often abusively and contributing to resistance that we will pay for in the future (we have already started to do so).
These infections, unlike other acute viral infections (measles, smallpox) or latent (varicella, mononucleosis) are characterized by partial immunity resulting from frequent mutations of the virus (genetic drift) that allows it to reinfect the host several times, although with a severity that is very limited by antibody-independent immunological processes.
All of them are contagious diseases – it is our experience that the flu/bronchitis/cold often spreads quickly in a family or in a work environment.
Flu or influenza is an epidemic seasonal viral pathology, due to the virus of the same name, of which there are several subtypes. For example, the 2009 virus was an H1N1, and for which there is a vaccine, although since the agent is easily mutated, it requires periodic boosters in order to keep up with the genetic drift of influenza (every year, the composition of the flu vaccine is updated and modified according to WHO regulations, in order to accompany the evolution of the virus).
Endemic coronaviruses, responsible for about 20% of common colds (the others are due to other viruses – rhinovirus and adenovirus mainly) were considered to be of minor importance compared to influenza until 2003.
Since November 2002, an atypical pneumonia has emerged in the Guangdong area (China), the cause of which was initially unknown, with a case fatality rate of around 10%. It was initially defined by clinical-epidemiological criteria (stay in an endemic area or risk contact plus fever above 38,5°C, plus drop in a certain type of white blood cells in the blood – lymphopenia plus bilateral pneumonia without response to antibiotics) and later named by the WHO with the name of “severe acute respiratory syndrome” (SARS).After an unprecedented scientific race, the responsible virus was identified in April 2003 and named SARS – CoV (SARS-associated coronavirus), and a test was later developed (PCR, however not in current use, and antibody assay) and a treatment (high-dose corticosteroid, several antivirals having also been tried, with inconclusive results). The outbreak ended up being limited in June of the same year, with more than 8.000 cases with 800 deaths (the number would certainly have been much higher, since there was no PCR test available for SARS-CoV,only the most severe cases were diagnosed, which inflated the perception of the severity of the disease). Later, SARS-like coronaviruses were identified in bats and civet cats in the region, so that transmission from animals to humans is assumed.
At the end of 2019, a SARS-like pathology emerged in Wuhan, and a new coronavirus of the same group (SARS-CoV-2) was identified. For fear of the economic repercussions of the term SARS, the WHO decided to call the pathology Covid-19 (from Coronavirus disease 2019), with the diagnostic criterion chosen being the positivity of the PCR test for the viral agent. This obviously makes the perception of the number of cases increase, with their severity being proportionately lower (in fact, the case fatality rate when applying the 2003 criteria to SARS-CoV-2 seems to be almost identical).
The two epidemics (SARS and Covid-19) have in common that they are the emergence of a new virus in a “virgin” population, which translates into greater contagiousness (because everyone is susceptible, although never the same, since we all carry the marks of exposure to other viruses – even other coronaviruses – that could limit the probability and severity of infection. (In fact, “virgin” populations are very rare – a good example of one was the Amerindians decimated by the smallpox brought by the Spanish conquerors).
As the population ceases to be a virgin (by vaccination and continued infection) the proportion of individuals with antibodies to the virus tends to increase and the severity and lethality decrease, as well as the risk of contagion – pandemic viruses tend to become seasonal (this was the case, for example, with the 2009 H1N1 and the 1968 H3N2, which are still the main seasonal influenza viruses today).
Therefore, it makes less and less sense to act based on the total number of cases given by PCR screenings, since this will always be very high (each individual has an average of 2 to 4 episodes of respiratory infection per year), and the epidemiological assessment should be made at the level of severity of these – hospitalizations and especially hospitalizations in intensive care motivated by the infection (and not hospitalizations for trauma that coincidentally have positive PCR for SARS-CoV-2).
Keeping the model of mass testing in an immune population unchanged can also be counterproductive to the functioning of general inpatient services without major benefits in preventing serious infection (imagine if everyone were regularly tested for herpes or influenza and isolated accordingly!) individual protection and testing is important, but now adapted to the risk of serious illness (e.g. patients undergoing chemotherapy, with malignant hematological disease-who have great difficulty responding to the vaccine, need care/screening that the general population could dismiss). It will also be important, especially in this subgroup of patients, to introduce antiviral drugs or specific immunotherapies that allow the infection to be treated, reducing the risk of complications.
Tiago Marques, Infectious Diseases Doctor
