Raised SARS-CoV-2 co-infection risk suggests other pathogens should not be overlooked

The increasing number of immunocompromised people exposed to COVID combined with the raised risk of co-infections of the SARS-CoV-2 virus and respiratory pathogens creates a double whammy that cannot be overlooked.

High hospitalisation rates of coronavirus infections among immunocompromised people still constitute a concern for public health even after the rollout of the COVID-vaccine campaign.

Immunocompromised people have weakened immune systems which affect the ability to fight infections and, in certain cases, even hamper the response to vaccines.

This condition exposes sufferers not only to COVID but to other pathogens as well.

“For instance, there is an increased risk of Legionnaire’s disease in those patients and I think there will be a lot more publications in the future that confirm that,” said Susanne Lee, a microbiologist with many years of experience in British public health agencies.

Legionnaires’ disease occurs by inhaling aerosols carrying the Legionella bacteria – which develop primarily in warm, stagnant water – with infection leading to a deadly form of pneumonia.

To make things worse, groups at risk from COVID-19 and Legionnaires’ disease are largely the same.

“There is also a risk that legionellosis might be misinterpreted or misdiagnosed as being COVID, due to the fact that symptoms can be quite similar to early Legionnaire’s diseases,” Lee told EURACTIV.

She added that getting a diagnosis quickly for legionellosis and getting the right antibiotics early could have a huge impact on a successful outcome from the disease.

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Co-infection risk

Another worrying aspect is co-infection risk and secondary infections of coronavirus and other pathogens, already observed during the 2009 influenza A (H1N1) epidemic.

At that time, the main concern was misdiagnosis due to availability bias, as treatable bacterial or parasitic infections were mistakenly labelled as influenza, research showed.

A case of co-infection of COVID-19 and legionellosis was first reported in Japan’s Asahi general hospital, where an 80-year-old Japanese national was hospitalised upon his return from a Nile cruise.

As symptoms of malaise, diarrhoea and cough had worsened after a week, the man was tested both for Legionella bacteria and for SARS-CoV-2 virus, resulting positive for both infections.

The Japanese man was in a risk group category as he had diabetes mellitus and died several weeks later, though the doctors who examined him, believed that the Legionella treatment was probably successful and that COVID-19 was the likely cause of death.

In a paper, the doctors who treated him highlighted the importance of differential diagnosis during the current COVID-19 pandemic, “so we do not miss the opportunity to diagnose other treatable causes of disease with similar symptoms.”

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‘Precautions are needed’

A study conducted in China’s Qingdao city on 68 patients with severe acute respiratory coronavirus confirmed the presence of other common respiratory pathogens.

Among those patients, 24 have been found to have other pathogens, such as influenza virus A (60%) and influenza virus B (53.3%), followed by mycoplasma pneumoniae (23.3%) and legionella pneumophila (20%) infection.

The research concluded that precautions are needed when dealing with COVID-19 patients who have coinfection with other respiratory pathogens.

A second study analysed urine samples from 93 patients infected with COVID from two tertiary-care hospitals in Germany. The Legionella pneumophila serogroup 1 antigen has been detected in a 41-year-old man with severe acute respiratory deficiency syndrome and bronchial asthma.

The main difference between the Chinese and the German study is that the first conducted cross-reactivity of indirect immunofluorescence tests with other bacterial species, while the latter was only focused on the detection of Legionella pneumophila serogroup 1 antigen.

There are 62 species of this bacteria known to date but Legionella pneumophila serogroup 1, causes most Legionnaires disease infections and the deadly form of pneumonia. In 2018, Legionella pneumophila amounted to 94.1% of confirmed cases in Europe.

“Detection of only L. pneumophila serogroup 1 antigen in urine is a suitable diagnostic approach for outpatient-acquired and travel-associated pneumonia, with varying sensitivity and specificity,” the author of the German study wrote.

A similar approach is suggested by health experts to check the presence of Legionella in the water system of public buildings.

In Annex III of the recently reformed EU’s drinking water directive, member states will be provided with the option of using alternative Legionella pneumophila testing – including focusing on Legionella pneumophila serogroup 1 – to achieve public health protection objectives.

“Clinicians treating patients positive for SARS-CoV-2 should be aware of possible co-infections with L. pneumophila and should use appropriate diagnostic approaches,” the author of the German study pointed out.

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[Edited by Benjamin Fox]

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