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Comment by philoph1122 | Hacker News Reader

It looks like the amount simply varies by season (high in winter, low in summer), unless I'm missing something...

First, in case it's not clear, these are (indirect measurements of) concentrations not volumes. There is a strong seasonal effect here, but it also tells other stories based on variations outside of that. Still, the seasonal bit is not unexpected, but hugely significant.

Most respiratory viruses, like influenza and colds have greater prevalence during the local winter. We'd expect COVID to behave similarly. The reasons for that are still debated.

In wastewater collection system, I&I (Inflow & Infiltration) is a constant problem where excess water from the environment enters the waste treatment pipeline. It's costly because all that otherwise clean water has to get the full treatment. So, it's interesting to me, that, unless they have normalized for I&I somehow which is not apparent in their raw data, the true seasonal variation in concentration is actually understated.

> So, it's interesting to me, that, unless they have normalized for I&I somehow which is not apparent in their raw data, the true seasonal variation in concentration is actually understated.

Biobot says:

"We normalize the SARS-CoV-2 viral concentration to a fecal indicator, to account for differences in dilution. We use PMMoV as this fecal indicator, which is an RNA virus that is commonly excreted in stool."

So they're effectively reporting on the ratio between SARS-CoV-2 and PMMoV concentration, which should be normalized for seasonal changes in dilution.

Ah thanks! I suspected it was done somehow, but it didn't jump out at me when I perused the raw data.

Coronavirus typically has a spike that starts in December and lasts until February. There are many theories about why this happens, but reduced Vitamin D levels has substantial proof behind it.

There's nothing "typical" about COVID19 yet.

But yes, there was a spike in December 2019, and another spike in December 2020. So we all are expecting a spike in December 2021.

Covid 19 is a kind of Coronavirus. Coronavirus is more than Covid 19, most if not all "cold" were caused by coronavirus

> most if not all "cold" were caused by coronavirus

No, just a significant minority:

https://www.webmd.com/cold-and-flu/cold-guide/common_cold_ca...

>There's nothing "typical" about COVID19 yet.

Corona viruses are a family of viruses that extends far beyond the particular virus responsible for the current pandemic/epidemic.

Corona viruses are the #2 family responsible for the common (viral) cold, behind rhinoviruses (In the ballpark of 10-20% and 50-60% respectively, iirc, but definitely rank #2 & #1).

So there is a great deal of historical knowledge about the corona family of viruses, just not necessarily specific to this corona virus and it's variants.

In the context of looking for seasonal patterns in respiratory viruses, it's the first place you'd look in trying to find common traits.

ETA: WebMD says 10-40% Rhino, 20% Corona, 20% RSV/parainfluenza, and 20-30% "other".

Last year cases started going up at least in November.

There is previous epidemiological history of other coronavirus variants, prior to the emergence of SARS-COV-2. That's what the comment above is referring to.

See for example:

"Epidemiology and Clinical Presentations of Human Coronavirus NL63 Infections in Hong Kong Children"

Authors: Ting Fan Leung, Chung Yi Li, Wai Yip Lam, Gary W. K. Wong, Edmund Cheuk, Margaret Ip, Pak Cheung Ng, and Paul K. S. Chan

ASM Journals, Journal of Clinical Microbiology, Vol. 47, No. 11

https://doi.org/10.1128/JCM.00832-09

https://journals.asm.org/doi/10.1128/jcm.00832-09?permanentl...

In the northern hemisphere? My theory is in spring/summer/fall people are hanging out outside, and as winter comes they think "I've been fine socializing the last few months, hanging out inside will be safe." and socialize indoors, where the lack of fresh air means the virus will spread...

This seems somewhat true based on spikes in the Southern US during the summer (people stay inside where there is AC), but doesn't seem to be the whole story. If that was the case, you would expect to see similar spikes in areas where there is say a week of rain (should be easy to measure in parts of Europe).

In my country - where for the last month we've basically had no sun, just clouds - there is a distinct spike around winter, which would follow nicely with the vitamin D theory. However in places like Southern Europe, which still has a good amount of sun during winter, there are similar spikes.

In some countries like Poland, covid looks like solely seasonal disease with nearly zero cases throughout the whole summer, and ramp up during autumn to peaks in winter and spring only broken with lockdowns, dropping back to near zero cases in the summer.

Its well known that COVID19 spreads more easily in the winter.

Because more people are getting sick with COVID19 at this time... it makes sense that more COVID19 samples will be found in wastewater.

Not to nitpick but I don't think that's what's well known. The virus' "behavior" doesn't change in the Winter. What changes is human behavior. We're inside less and inside more, and that typically means we end up in closer (enclosed) quarters with others.

Perhaps that's what you meant?

I think you have a valid theory, but... its not 100% clear if that's the only case.

Viruses could literally be affected by the lesser amounts of sun and shorter days. UV-rays kill the virus for instance, and we get less of them in the winter than during the summer.

Without knowing any more details on "why" there's a relationship between COVID and the winter (whether its human behavior that changes, or if its physically something associated with the virus / sun... like day length + UV rays or heat vs humidity), we just have to say the most generic thing possible to remain correct.

In this case: we know that COVID19 seems to spread more in the winter. We have lots of theories why this happens, but I personally haven't seen any "Mythbusters" style study that goes over all the theories and actually proves any of them.

The humidity inside buildings changes with the outdoor temperature, since cold air carries less water and heaters don't add that back unless you use a humidifier. Isn't that one of the theories behind transmission changing with the seasons?

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