# How many viruses do I need to inhale to catch a cold? **URL:** \ **Category:** Factual Questions\ **Created:** [November 21, 2007, 3:03pm UTC](https://boards.straightdope.com/t/how-many-viruses-do-i-need-to-inhale-to-catch-a-cold/427324 "2007-11-21T15:03:34Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![solkoe](https://avatars.discourse-cdn.com/v4/letter/s/919ad9/32.png) [@solkoe](https://boards.straightdope.com/u/solkoe)\ **Post date:** [November 21, 2007, 3:03pm UTC](https://boards.straightdope.com/t/how-many-viruses-do-i-need-to-inhale-to-catch-a-cold/427324/1 "2007-11-21T15:03:34Z")
If I breathe in one cold virus will I catch a cold? I know that one virus can make millions so I suppose it is possible. I vaguely remember learning about something called _titre_ in university which states that a certain quantity of virus is needed to infect a sample but I don’t understand the concept. Any help? ---
**Author:** ![solkoe](https://avatars.discourse-cdn.com/v4/letter/s/919ad9/32.png) [@solkoe](https://boards.straightdope.com/u/solkoe)\ **Post date:** [November 22, 2007, 1:32pm UTC](https://boards.straightdope.com/t/how-many-viruses-do-i-need-to-inhale-to-catch-a-cold/427324/2 "2007-11-22T13:32:22Z")
Putting this out there one more time. ---
**Author:** ![picunurse](https://avatars.discourse-cdn.com/v4/letter/p/7bcc69/32.png) [@picunurse](https://boards.straightdope.com/u/picunurse)\ **Post date:** [November 22, 2007, 4:10pm UTC](https://boards.straightdope.com/t/how-many-viruses-do-i-need-to-inhale-to-catch-a-cold/427324/3 "2007-11-22T16:10:34Z")
It depends on the “cold” virus you’re exposed to. There are over 100 strains of [Rhinovirus](http://www.emedicine.com/ped/topic2707.htm), that’s just one group that causes upper respiratory symptoms. [Respritory Syncytial virus](http://www.cdc.gov/ncidod/EID/vol10no6/03-0629.htm) causes cold symptoms in adults, but can be life threatening in infants. Also, viruses don’t really hang out alone. If you’re exposed, it’s likely you’re exposed to a few million. ---
**Author:** ![Bob55](https://avatars.discourse-cdn.com/v4/letter/b/e9c0ed/32.png) [@Bob55](https://boards.straightdope.com/u/Bob55)\ **Post date:** [November 22, 2007, 5:09pm UTC](https://boards.straightdope.com/t/how-many-viruses-do-i-need-to-inhale-to-catch-a-cold/427324/4 "2007-11-22T17:09:15Z")
The common cold is caused by over 200 agents. Rhinovirus causes about 50%, coronavirus another 20%. What you’re looking for is called the Infectious Dose, or ID50 (the number of organisms it takes to cause infection in 50% of test subjects). Usually viruses and bacteria have ID50s of 100,000+, either because they need to overwhelm your immune system, or create biofilms to stick and invade. I teach Microbiology, and one book I use (Tortuga, Funke, and Case) says that the infectious dose for rhinovirus is only one. [This PDF](http://www.ifh-homehygiene.org/2003/2library/ecless.pdf) seems to confirm this: > [@](#): > > Indications are that cold viruses deposited on surfaces, either from the hands or the settling of aerosol particles, can remain viable on that surface – and in large numbers – for several hours (Gwaltney and Hendley 1982, Sattar et al. 1993). By contrast with bacteria the “infectious dose” i.e the number of viral particles required to cause infection may be very small (Smith et al. 1966, Couch 1990). For rhinovirus the infective dose may be less than 1 TCID (Couch 1990). ---
**Author:** ![aldiboronti](https://avatars.discourse-cdn.com/v4/letter/a/9fc348/32.png) [@aldiboronti](https://boards.straightdope.com/u/aldiboronti)\ **Post date:** [November 22, 2007, 5:35pm UTC](https://boards.straightdope.com/t/how-many-viruses-do-i-need-to-inhale-to-catch-a-cold/427324/5 "2007-11-22T17:35:34Z")
I recall reading that you can only catch each strain once, in other words, once you’ve had a couple of hundred colds, you’re immune. Of course, even if true, it doesn’t make a great deal of difference, I guess - that’s enough to last a lifetime and more anyway. ---
**Author:** ![Chasing\_Dreams](https://avatars.discourse-cdn.com/v4/letter/c/258eb7/32.png) [@Chasing\_Dreams](https://boards.straightdope.com/u/Chasing_Dreams)\ **Post date:** [November 22, 2007, 6:33pm UTC](https://boards.straightdope.com/t/how-many-viruses-do-i-need-to-inhale-to-catch-a-cold/427324/6 "2007-11-22T18:33:42Z")
[QUOTE=aldiboronti] I recall reading that you can only catch each strain once, in other words, once you’ve had a couple of hundred colds, you’re immune. Of course, even if true, it doesn’t make a great deal of difference, I guess - that’s enough to last a lifetime and more anyway. [/QUOTE] Why don’t we just infect ourselves with all 200+ strains at once and be done with it? ---
**Author:** ![Bosda\_Di\_Chi\_of\_Tricor](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bosda_di_chi_of_tricor/32/16845_2.png) [@Bosda\_Di\_Chi\_of\_Tricor](https://boards.straightdope.com/u/Bosda_Di_Chi_of_Tricor)\ **Post date:** [November 22, 2007, 7:35pm UTC](https://boards.straightdope.com/t/how-many-viruses-do-i-need-to-inhale-to-catch-a-cold/427324/7 "2007-11-22T19:35:38Z")
And, on this general topic, a happy-slappy note from Hell— [http://www.pcmag.com/article2/0,2704,2218166,00.asp](http://www.pcmag.com/article2/0,2704,2218166,00.asp) > [@](#): > > WASHINGTON (Reuters) - A new and virulent strain of adenovirus, which frequently causes the common cold, killed 10 people in parts of the United States earlier this year and put dozens into hospitals, U.S. health officials said on Thursday. > > A U.S. Centers for Disease Control and Prevention report detailed cases of people ill in May of 2006 and from March to June of 2007 with a strain of the virus called adenovirus 14 in New York, Oregon, Washington state and Texas. > > “What makes this particular adenovirus a little different is that it has the capability of making healthy young adults severely ill. And that’s unusual for an adenovirus, and that’s why it’s got our attention,” Su said in a telephone interview. > > Two of the 10 people who died from the new strain were infants, Su said. The CDC report said about 140 people were sickened by the virus and more than 50 hospitalized, including 24 admitted to intensive care units. ---
**Author:** ![Otto](https://avatars.discourse-cdn.com/v4/letter/o/bbe5ce/32.png) [@Otto](https://boards.straightdope.com/u/Otto)\ **Post date:** [November 22, 2007, 7:50pm UTC](https://boards.straightdope.com/t/how-many-viruses-do-i-need-to-inhale-to-catch-a-cold/427324/8 "2007-11-22T19:50:30Z")
I asked a similar question a while back and thought it might be germane to the topic of this thread. Turns out it’s not, but it took so goddamn long to search for it that I’m posting a link to it anyway. [Did Charlie Brown lie to me about the common cold?](http://boards.straightdope.com/sdmb/showthread.php?t=215750) ---
**Author:** ![Smeghead](https://avatars.discourse-cdn.com/v4/letter/s/f1d935/32.png) [@Smeghead](https://boards.straightdope.com/u/Smeghead)\ **Post date:** [November 22, 2007, 8:00pm UTC](https://boards.straightdope.com/t/how-many-viruses-do-i-need-to-inhale-to-catch-a-cold/427324/9 "2007-11-22T20:00:49Z")
[QUOTE=aldiboronti] I recall reading that you can only catch each strain once, in other words, once you’ve had a couple of hundred colds, you’re immune. Of course, even if true, it doesn’t make a great deal of difference, I guess - that’s enough to last a lifetime and more anyway. [/QUOTE] It’s not true. The memory cells that live in your mucous membranes only last a few months, as opposed to the ones in your blood that last pretty much forever.