Answer by Researcher davidsarokin on Tue 9 Oct 2007 - 3:26 am UTC:

upstill,

Interesting question, and one that (believe it or not) I've wondered about
myself.

As you're already well-aware, washing ones hands is considered de rigueur
in the public health community, as a means of reducing transmission of
infectious diseases.  

The practice stems from a combination of good medical science, common
sense, pragmatism, and social etiquette.

In a nutshell, we certainly know enough about disease transmission to
strongly recommend hand-washing as a reasonable public health measure.  

Not much is really known about the specifics of many common diseases, in
terms of the relative importance of contamination from, say, door knobs vs
shaking hands, sneezing vs wiping, and so on. So it's hard to quantify the
specific role of urination as a means of disease transmission. 

Your question contained a big caveat:  "assuming that nobody's peeing on
the hands". Nobody's pooping on their hands either, at least not
intentionally.  But a person's hands can certainly, if inadvertently, come
in contact with urine as well as feces, so I've kept this possibility in
consideration in answering your question.  

Bottom line: disease organisms can certainly get onto the hands during
urination from either skin or from urine, and these can then lead to
disease transmission.  How big a contributor this is to overall disease
transmission is not known, but I didn't come across anything to suggest it
rivals contamination from fecal matter as a contributor to disease.  But
even if urination is not a big contributor, the recommendation to wash
hands after any restroom use is a sensible one, simply because restrooms
are where sinks are located...the several visits that people typically make
a day are the ideal occasion to wash hands, and lower the germ count.  


For starters, a bit of background on the history of hand-washing and public
health:


http://www.cdc.gov/od/oc/media/pressrel/r2k0306c.htm
Why is handwashing important?

"...Remember Ignaz Semmelweis? Of course you don't. But you're in his debt
nonetheless, because it was Dr. Semmelweis who first demonstrated over a
hundred years ago that routine handwashing can prevent the spread of
disease.

...In an experiment considered quaint at best by his colleagues, Dr.
Semmelweis insisted that his students wash their hands before treating the
mothers--and deaths on the maternity ward fell fivefold. 

..."This was the beginning of infection control," Dr. Gerberding said. "It
was really a landmark achievement, not just in healthcare settings, but in
public health in general because today the value of handwashing in
preventing disease is recognized in the community, in schools, in child
care settings, and in eating establishments."



As pinkfreud noted in a comment, above, the warm, moist groin area is
generally a beehive of bacterial activity: 

http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=170588
Aerobic microbial flora of intertrigenous skin.

"...The incidence of gram-negative rods was 17% for the axilla, 13% for the
groin, 10% for the toe web, and 9% for the finger web. Klebsiella, Proteus,
and Enterobacter were the predominant organisms, in that order. The highest
incidence of Staphylococcus aureus was in the groin (12%) and toe web
(11%)."


Oral-genital sex can also be a route of disease tranmission:

http://www.cdcnpin.org/scripts/std/std.asp
STDs Today

"...Chlamydia can be transmitted during vaginal, oral, or anal sexual
contact with an infected partner. 

...HSV type 1 most commonly causes sores on the lips (known as fever
blisters or cold sores), but it can cause genital infections through
oral-genital or genital-genital contact.

...Syphilis is passed from person to person through direct contact with a
syphilis sore...Transmission of the organism occurs during vaginal, anal,
or oral sex."


Human urine is normally thought to be pretty clean stuff:

http://www.bio.net/bionet/mm/microbiology/1998-January/011380.html
Human urine normal flora

"...The reason human urine in the bladder is usually sterile is because
it's never exposed to bacteria."


However, research is beginning to show it may not be as prisine as is
commonly thought:

http://jcm.asm.org/cgi/content/abstract/42/2/753
Viable but Nonculturable Bacteria Are Present in Mouse and Human Urine
Specimens 

"...Urine specimens obtained from human female volunteers with or without
an active urinary tract infection were found to contain, on average,
significantly more viable than culturable forms of bacteria."
[NOTE: Meaning that the urine might look sterile, but actually not be, as
it contains organisms that don't show up during laboratory cultures]


At least several diseases are thought to be transmitted (at least partly)
through contact with human urine:

http://dhfs.wisconsin.gov/communicable/factsheets/Handwashing.htm
Disease Fact Sheet Series: Hand washing 

"...Diseases may also be spread when hands are contaminated with urine,
saliva or other moist body substances. Microorganisms which may be
transmitted by one or more of these body substances include
cytomegalovirus, typhoid, staphylococcal organisms, and Epstein-barr virus.
These germs may be transmitted from person to person or indirectly by
contamination of food or inanimate objects such as toys. "


http://findarticles.com/p/articles/mi_m0CYP/is_9_110/ai_94261104
Disease transmission models for public health decision making

"...The life cycle of the schistosome begins with the sexual pairing of
adult worms in the blood vessels of the host and the production of copious
numbers of eggs, a fraction of which are excreted in feces (or urine in the
case of S. haematobium)"


http://carc.ucsc.edu/Health%20and%20Safety/Zoonosis/Wild%20Rodents.htm
Wild Rodents and Rabbits: Potential Zoonotic Diseases

"...Lymphocytic choriomeningitis (LCM) is caused by the arenavirus commonly
associated with hamsters, but does infect mice... Transmission to humans is
through contact with tissues including tumor, feces, urine, or
aerosolization of any one of these."


http://www.leptospirosis.org/topic.php?t=17
The Leptospirosis Information Center

"...In humans, viable bacteria will be present in the urine after about 2
days from the exposure (day E2), and they will usually remain present for a
few weeks after illness, but there are recorded cases of humans shedding
the bacteria for up to 11 months. Treatment with antibiotics can reduce the
symptoms and also reduce this shedding time, but in most patients their
urine contains detectable bacteria for many weeks after clinical recovery.
Our advice is to assume some risk from urine for up to 12 months after the
acute illness has faded."


http://www.journals.uchicago.edu/CID/journal/issues/v32n3/000858/000858.html
HEMORRHAGIC FEVERS DUE TO CRIMEAN-CONGO HEMORRHAGIC FEVER, EBOLA, LASSA,
AND MARBURG VIRUSES 

"...Transmission of Viral hemorrhagic fever (VHF)...has been associated
with reuse of unsterile needles and syringes and with provision of patient
care without appropriate barrier precautions to prevent exposure to blood
and other body fluids that contain the virus (including vomitus, urine, and
stool)"


On the other hand, the presence of disease organisms in urine does not
always lead to demonstrable routes of infections. Medical researchers often
can't say one way or the other whether contact with urine would be a
significant -- or even a possible -- route of transmittal:

http://www.ento.psu.edu/Lyme/default.htm
Lyme Disease - Introduction & Disease Transmission 

"...Although in theory Lyme disease could spread through blood transfusions
or other contact with infected blood or urine, no such transmission has
been documented. There is no evidence that a person can get Lyme disease
from the air, food or water, from sexual contact or directly from wild or
domestic animals."


http://www.journals.uchicago.edu/CID/journal/issues/v37n10/31839/31839.html
Does Contact with Urine and Blood from a Rabid Dog Represent a Rabies Risk?


"...Human-to-human transmission of rabies once a patient with rabies has
been admitted to a hospital has always been a serious concern. Other than
the report of transmission via corneal transplantation, there are no
reliable reports of such transmission [1]. Although rabies virus has been
isolated from urine sediment after centrifugation (in 1 of 8 samples) [7],
and although the detection of rabies virus RNA in urine samples is as
accurate a diagnostic tool as its detection in saliva samples [5], we
failed to demonstrate the infectivity of urine"


http://www.blackwellpublishing.com/eccmid17/abstract.asp?id=56110
Risk assessment and management of possible transmission of Lassa virus
during two flights

"...During the two flights the patient had no cough but a urinary tract
catheter which was disconnected from the reservoir and released relevant
amounts of urine on the passenger's seat. The patient's urine was tested
positive for Lassa virus, which was taken into account for the risk
assessment and contributed to the decision to trace back co-passengers
potentially exposed.

...In this investigation, the leakage from the urinary catheter reservoir
influenced the risk assessment and the decision for a passenger trace back
as Lassa fever is primarily transmitted by urine of rats. Nevertheless, no
contact passenger revealed Lassa virus. Our investigation confirms that the
human to human transmission of Lassa virus during flights is unlikely if no
haemorrhagic symptoms appear at this time."


And for an ironic twist, hand-washing might increase the danger of certain
infection routes, if the disease organisms are not destroyed after they go
down the drain:


http://yosemite.epa.gov/opa/admpress.nsf/0de87f2b4bcbe56e852572a000651fde/cafc5c6829e5ae708525732200511786!OpenDocument
Fecal Bacteria and Human Viruses Found in Upper Florida Keys 

"...Genetic material from intestinal viruses, which can cause disease and
are spread through infected human feces and urine, were found throughout
the sampled area

...The detection of these bacteria near shore suggests that land-based
sources of sewage pollution, like cesspits and septic systems, may be
significant contributors."


=============================================================


All this boils down to a lot of possible ways that the simple act of
urination could lead to contaminated hands, and to transmission of disease.
 It doesn't tell us, though, how often this happens, or how significant a
route of transmission this might be. 

However, if you were sitting on the plane next to the sick guy with the
leaky catheter...wouldn't you be just a wee bit worried?


Let me know if there's anything more you need on this.

David