How we protect ourselves from infections

We live our everyday lives together with countless microbes and viruses that could also infect us. The immune system prevents many attacks, but it needs our cooperation: Proper hygiene and regular vaccinations effectively protect against infections.

Viruses, bacteria, fungi and yeasts are lurking everywhere. Whether at home or work, in the hospital or even on or in human bodies – they can be found on every centimetre of every surface on Earth. The vast majority of microorganisms and viruses, which are not counted as living creatures, cannot harm us. Quite the opposite: Microbes are extremely useful in breaking down waste and toxic substances or, as intestinal flora, supporting our digestion. However, a few species may also cause infections, specifically if they reach the body at the wrong place or in a too large number.

We are exposed to microorganisms anywhere in our environment, because they are omnipresent. Litter bins, cleaning rags or the refrigerator characterised by their combination of moisture and food leftovers are specifically preferred places for growth of microorganisms. Bacteria and fungi especially reside and grow in open-ended food, for example in juice bottles that have been opened but not kept refrigerated or on wooden chopping boards, where bacteria such as Campylobacter or Salmonella, the most common causes of gastrointestinal infections, can often be found after handling poultry.

"Bacteria are necessary for training the immune system, too. This is why we cannot and should not live in a sterile world."

Dietmar Pieper, head of the “Microbial Interactions and Processes” research group

In fact, the human body is so attractive to microorganisms that the number of microbial inhabitants exceeds that of the human cells. For example, staphylococci are the most prevalent natural colonisers on the skin and in the nasopharyngeal cavity. However, staphylococci and specifically Staphylococcus aureus can also cause serious wound infections. MRSA (Methicillin-resistant Staphylococcus aureus) is resistant to common antibiotics and thus extremely difficult to treat. About 20 per cent of the human population carry Staphylococcus aureus in their nose, without being aware of it – but is that a reason for panic? Dietmar Pieper, head of the “Microbial Interactions and Processes” research group at the Helmholtz Centre for Infection Research (HZI), answers with a decisive ‘no’: “Bacteria are necessary for training the immune system, too. This is why we cannot and should not live in a sterile world.” However, multi-resistant bacteria such as MRSA pose a threat, and require stricter hygiene measures – also to protect other humans.

Day-to-day protection

Our everyday lives confront us with many potential risks for infections, and often these cannot be avoided. “A shipment of food can sometimes be contaminated, for example with listeria,” says Pieper. “Protection against it is difficult, because such a case is relatively rare and you cannot see it in the food.” To minimise the risk, the microbiologist warns against eating any spoiled food in which both bacteria and fungi can grow and form toxins. In addition: “Foreign countries, foreign microbes. Therefore it is safer to prefer cooked food,” says Pieper. A frequent path of infection is via the hands, as they may collect germs from different surfaces and transfer them to the mouth or nose. This contact infection can also transmit viruses including influenza or gastrointestinal bacteria such as Escherichia coli, but most environmental bacteria are harmless. The best protection is also the most simple: “In everyday life, regular hand washing with soap is more than sufficient; this is also better for the skin than disinfectants,” says Pieper.

However, hand washing needs to be done properly. Quickly holding your fingers under the tap is not enough. The health authorities recommend holding your hands under running water, rubbing them with soap for 20 to 30 seconds, rinsing them again under running water, then drying them using paper towels or your own personal hand towel. In order to avoid infections, it is important to wash your hands every time you blow your nose, use the toilet, stroke an animal or handle raw meat.

Arming the immune system against tricksters

Viruses are particularly adept at taking over a human body. They change quickly and constantly surprise the immune system with new disguises. This means that the immune cells only register them as pathogenic once the infection is already underway. But the immune system can remember some pathogens for a lifetime; these include the rubella virus and the measles virus, which is responsible for the recent measles outbreaks. The immune system has a good memory that can be strengthened in these cases, without the need to first suffer through the sometimes life-threatening infections: “Vaccinations, along with hygiene and access to clean water, are one of the most important elements in preventing infections,” says Berit Lange, medical doctor and epidemiologist at the HZI “Epidemiology” department. “A good vaccine can even eradicate a pathogen.”

"Vaccinations, along with hygiene and access to clean water, are one of the most important elements in preventing infections,"

Berit Lange,  medical doctor and epidemiologist at the HZI “Epidemiology” department.

Vaccination has already achieved some major successes, such as the eradication of smallpox. The poliovirus, which causes infantile paralysis, has also largely disappeared. Thanks to consistent vaccination programmes, Germany has been polio-free since 1990 – with two last imported cases in 1992. Polio infections with the wild virus only occur in Pakistan and Afghanistan, from where the viruses could be spread to other countries, and therefore vaccination is still necessary. A prerequisite for the eradication of a pathogen with human-to-human transmission is herd immunity: This occurs when so many people are vaccinated or immune that individual cases of infection do not spread further. The level of coverage required depends on how effective the vaccine is, and how easy or complicated it is to transmit the pathogen required for infection. “In the case of measles, the necessary vaccination coverage is quite high at 95 per cent, even though the vaccine is very effective,” says Berit Lange. “This is because one person with measles infects an average of 15 others.”

Should vaccination be compulsory?

The Robert Koch Institute found that a decreasing number of children have been vaccinated recently: Since 2014, the rates of standard vaccinations against tetanus, diphtheria, whooping cough and polio have declined slightly. For measles, the vaccination rate has stagnated at a level that is too low, especially for the second vaccination, which means that there is still no herd immunity. Full protection can only be obtained after two vaccinations. This also applies to mumps, rubella and chickenpox. “The willingness to vaccinate and the vaccination coverage against measles in Germany is by no means bad, but it is still not high enough to eliminate measles,” says Lange. According to the World Health Organization (WHO), at least 95 per cent of the population must be vaccinated twice to eliminate measles. Germans have only achieved this figure for the first vaccination, with a total of 97.1 per cent, while the rate for the second vaccination has stagnated at 92.8 per cent (2016, 2017). So far, only two federal states have broken the 95 per cent mark for both vaccinations: Mecklenburg-Vorpommern and Brandenburg. Baden-Württemberg is the worst performer nationwide, with only 89.1 percent. The goal of eradicating measles cannot be achieved with these numbers, which, given the regional outbreaks of measles, has now led to the introduction of compulsory vaccination.

“As a doctor, I would rather convince people to get vaccinated than force them. From a healthcare perspective and as a researcher, I can understand the introduction of compulsory vaccination. But I find it disappointing that this step was felt to be necessary,” says Berit Lange. “I think that it is right, however, that only vaccinated children can be accepted into childcare centres – especially with children under the age of three – in order to protect the children who cannot be vaccinated.” It is also important that the centres know which of the registered children are vaccinated and which are not. “This documentation will certainly be improved by the new law.”

The “Epidemiology” department at the HZI is researching how to ensure that vaccines and vaccination campaigns remain safe and lead to the highest possible vaccination coverage. For example, a project team, led by Lange’s colleague Jördis Ott, has developed the “SafeVac” app as part of a study, and is now investigating how successfully it can be used to monitor symptoms after an influenza vaccination. Berit Lange and colleagues at the University Hospital in Freiburg are investigating how diseases that we could be protected against by vaccination can best be prevented in more susceptible population groups. Previously, Lange and her international partners had investigated the safety of rubella vaccination in pregnant women who were not supposed to be vaccinated. In a meta-analysis of the scientific literature to date, however, she was unable to find any indications of vaccine-associated malformations in the babies of pregnant women who had been vaccinated accidentally.

Hospitals as germ factories

More and more pathogens are becoming resistant to antibiotics. This is specifically due to the excessive use of antibiotics, for example in animal breeding and in patients that do not need antibiotics such as in the case of colds caused by viruses. Antibiotics only fight bacteria and are completely ineffective against viruses. Used incorrectly, antibiotics only encourage the development of resistance. “Bacteria can mutate or take up foreign DNA, resulting in the natural development of antibiotic resistance,” says Dietmar Pieper. “That is why resistant bacteria are found everywhere and in each one of us.” Resistant bacteria may also develop in hospitals and can further spread through inadequate hygiene and also via wastewater. “Proper hygiene measures are critical when dealing with patients. Thorough hand washing and disinfection after each patient contact must be routine,” says Pieper. But good hygiene also relies on properly trained medical personnel. “In the Netherlands, every patient in the hospital is tested for carriage of MRSA – with the result that hospital acquired infections with this pathogen are far less common there,” says Pieper.

„Practically, strains of all bacteria on and in us are under unknown instances capable of triggering an infection, for example in severely immunocompromised people. However, no one should fear these microbes, as life without them is impossible.“

Dietmar Pieper

Although good hygiene effectively protects against infections in clinics and everyday life, infections cannot be prevented. “Often the real niche of the infectious agent remains unknown,” says Dietmar Pieper. An example is necrotising fasciitis, which can be caused by Streptococcus pyogenes and typically affects healthy people. In many cases, however, it is caused by a mixed infection that also leads to the rapid destruction of the affected tissue. In collaboration with Eva Medina’s team at the HZI Pieper investigated the microbial community causing necrotising fasciitis, as part of a large-scale EU project (INFECT). They discovered that the bacteria that trigger the disease are mostly otherwise harmless inhabitants of the body that for unknown reasons switch to a destruction mode. “Just by working together they are able to colonise the host tissue and strengthen a destructive, inflammatory immune response,” says Eva Medina, who heads the “Infection Immunology” research group at the HZI. Dietmar Pieper adds: “Practically, strains of all bacteria on and in us are under unknown instances capable of triggering an infection, for example in severely immunocompromised people. However, no one should fear these microbes, as life without them is impossible.”

Author: Andreas Fischer

Published: November 2019


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Dr Andreas Fischer

Science Editor (deputy Spokesperson)

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