In a community study of healthy infants reported in 2015, the authors stated that “Our finding of low RSV prevalence in asymptomatic infants suggests that RSV is likely the causative agent when detected in the setting of clinical symptoms of bronchiolitis. By contrast, given the observed prevalence of rhinovirus in infants without ARI, and even in infants without any respiratory symptoms, it remains unclear if rhinovirus detection always reflects current illness.”[1] 

To paraphrase, we don’t think rhinoviruses (HRVs) play much of a role in causing bronchiolitis in this study of children who didn’t have bronchiolitis, because we found HRV more often in healthy kids than HRSV (human respiratory syncytial virus).

This topic tends to make me talk loudly, even more quickly than normal, and spit a bit.

Right. Let’s take this from the top.

• “Rhinovirus” is not one virus.
  I went into a bit of detail in my last post. It might have been a bit deep, confusing or just boring for some, though. The HRVs comprise three species (A, B, C) and about 167 genotypically distinct viruses.[4] While we don’t have serotype data for all of them (the discovery of a third species in 2007 was based entirely on genetics, not proteins), before the HRV-Cs, we knew that our immune systems recognised> 100 HRVs as distinct viruses. This also assumes that each of the 167 HRVs is not continuing to evolve. But they are continuing to evolve. This evolution likely includes changes at their antigenic sites, which may help them appear “new” to the memory bits of our immune system.
• HRSV consists of at least 2 antigenically distinct viruses (probably more).[2]
  See the earlier post for some details about antigens.[3]
• This study treated HRV and HRSV as single viruses. Among these healthy infants, RSV (2 or more viruses) was rare, whereas HRVs (167 or more viruses) were more common.
• This study found 16 HRVs (14.5% of infants): 6 HRV-A viruses, 1 HRV-B, 8 HRV-C, and 1 untypeable HRV. At least 4 different HRV genotypes representing all three RV species (A-C) were presented.
• The authors didn’t spell this out, but there were probably a few different genotypes within each species as well
• The authors found that 1.8% of infants were HRSV-positive (2 of 110). By species, 5.5% were HRV-A positive, 0.9% were RV-B positive, and 7.3% were HRV-C positive. So, to follow the logic, HRSV was twice as likely to be found in these healthy infants as an HRV-B! What if there were 2 or more distinct HRV-Bs? H
  HRSV – an agreed-upon serious respiratory pathogen of infants, children, adults and the elderly, is more often found in healthy infants than the wimpiest of the RVs? Hmmm. Wonder why that didn’t make the title. HRSVs must have a good agent.

ASIDE: RV-Bs are considered by those in the HRV world, including at least one of the authors of this study, to be the least often detected (disproportionately so [13]) and least threatening pathogens among the common cold viruses.[6,7,8,9,10,12] It would be interesting to immunologically compare a goodly number of RV-As and -Bs, as was done for a few HRVs (grouped in a different way) in a 2009 study. This might show whether members of the HRV-B are less effective at killing their host cells and triggering an immune response that leads to inflammation.[11]. 

This all highlights an important issue. We’ll never understand what HRVs are capable of if we only look at them as a group. We’ll understand even less if we don’t include testing for them on samples from ill patients with respiratory signs and symptoms. Testing is expensive, of course, so it will remain a piecemeal process until there is a treatment or vaccine.

When we comprehend that HRVs are a large array of distinct, independently circulating viruses, we will likely find that each infection with a single HRV genotype can result in…

• no illness at all or
• mild illness or
• moderate illness or
• severe illness

…at rates similar to any other ‘serious’ respiratory virus, be that RSV or an influenza virus.

If we only look at the HRVs as a group, we’ll miss these patterns and never learn more.

Given that our understanding remains based on virus detection data from an age of insensitive laboratory methods from decades ago, continuing as we have would be very short-sighted indeed. Not only short-sighted, but it will lead us to the wrong conclusions, like the one in the title above.

By all means, leave your thoughts in the comment box below or engage with me on Bluesky @mackayim.bsk.social

References…

1. Detection of respiratory syncytial virus and rhinovirus in healthy infants.
   https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4660840/.
2. Sequence variability of the respiratory syncytial virus (RSV) fusion gene among contemporary and historical genotypes of RSV/A and RSV/B.
   http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0175792
3. Human respiratory syncytial virus: an example of why calling them many usually outweighs calling them few, or one
   https://wp.me/p96NBC-TK
4. http://www.picornaviridae.com/enterovirus/enterovirus.htm 
5. Brief info about on what an antigen is
   https://virologydownunder.com/human-respiratory-syncytial-virus-an-example-of-why-calling-them-many-usually-outweighs-calling-them-few-or-one/#antigen
6. Human Rhinovirus Species and Season of Infection Determine Illness Severity
   https://www.ncbi.nlm.nih.gov/pubmed/22923659
7. Clinical and molecular features of human rhinovirus C
   https://www.ncbi.nlm.nih.gov/pubmed/22285901
8. A novel group of rhinoviruses is associated with asthma hospitalizations
   https://www.ncbi.nlm.nih.gov/pubmed/19027147
9. Do rhinoviruses reduce the probability of viral co-detection during acute respiratory tract infections?
   https://www.ncbi.nlm.nih.gov/pubmed/19376742
10. Assessment of wheezing frequency and viral etiology on childhood and adolescent asthma risk
    http://www.jacionline.org/article/S0091-6749(16)30897-1/fulltext
11. Diversity in the bronchial epithelial cell response to infection with different rhinovirus strains
    https://www.ncbi.nlm.nih.gov/pubmed/19207121
12. From sneeze to wheeze: What we know about rhinovirus Cs
    https://www.ncbi.nlm.nih.gov/pubmed/23714395
13. Newly identified respiratory viruses in children with asthma exacerbation not requiring admission to hospital
    https://www.ncbi.nlm.nih.gov/pubmed/20572080

Updates

1. 28JUN2026. Improved grammar, SEO and updated formatting