How deadly should infected wounds be, on average?

[KarlKost]

Originally Posted by mlangsdorf

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1281639/ says that at London hospitals in the 1850s, the survival rate for surgical amputations was around 60%. That's a bad case for surviving an infection: non-sterile operating and recovery environments, no anti-biotics, but some attempts at post-operation care. Though I'm not really sure how much difference the care made.

When I flipped my bicycle and broke everything, my shoulder wound got infected despite thorough attention by the trauma docs[1]. Even so, that was treated more as annoying and gross instead of life-threatening, and it actually took a follow-up visit or two to get anti-biotics prescribed. On the other hand, it did not go away on its own at all.

If you're looking for a harsh realism game, infected wounds should probably do 1 HP/day, resisted at some HT penalty sufficient to kill about 40% of the HT 10 population - I don't know what that number is. Possibly with some symptoms that include additional HT penalties, so the people who fight the infection off early are okay, but there's a rapid down spiral if the infection isn't resisted early on. It'd probably make the math easier.

[1] The rules on B444 for catching an infection seem too generous, based on my limited experience. I only had 1-2 open wounds, was hospitalized, and still got an infection. Maybe my surgeon critically failed the Physician roll, but I'd say for harsh realism games, people need to roll to resist infection even at TL 6+.

On the other hand, given some of the other oddities of my medical history, maybe I just have Unlucky (Medical issues only) [-1] and the infection was just a result of that.

An HT roll of 10 has a success chance of 50%. At 9 HT, the success chance is at 37.5%. So in order to have a more or less 40% chance of failure in a single roll, it would actually have to be more or less HT 11.

If however you need to roll every day, with success meaning no damage and failure meaning 1 HP, with possibly 2 HP on a crit failure, and end of infection only after a crit success, that's more than enough. Let's see:

HT 10
Crit Success Chance (3/4)
Number of Rolls
__1._____2._____3._____4._____5.______6.______7.__ _
1.85%_3.67%_5.45%_7.20%_8.91%_10.60%_12.25%

___8.______9._____10._____11.______12._____13.__
13.88%_15.47%_17.03%_18.57% _20.07%_21.55%

__14._____15._____16._____17._____18._____19.__
23.00%_24.43%_25.83%_27.20%_28.55%_29.87%

__20.__
31.17%

So, as you can see, the chance of achieving a critical success (3 or 4) after 20 days (rolls) is only of around 30%, still far from the needed 60% of success rate required (to have a 40% rate of failure).
And, if success at the HT roll on a day means no damage, while failure means 1 HT loss, that means that after 20 days the victims will have taken an average of 10 HP of damage, being reduced to 0. And you have 30% chance of having at least 1 critical failure (17/18) over that time.

At a maximum of 40 rolls (40 days), you'll suffer an average of at least 20 HP of damage, enough to take you to -1 × HP, and the chance of achieving success (roll of 3 or 4) at least once in that time is:

1 - 0.9815^40 = 52.62%, or almost 50% chance of success.

And if the sick fails all those rolls, it invariably reaches -1×HT, going to the first roll to stay alive, which is also done at 50% (HT 10)

So, with a probably of more or less 50% of recovering all the way up to reaching the first threshold of death, and 50% chance to surviving it, the possibility of (eventually) recovering is around 75%, so this is a fine metric, despite seeing as if requiring a critical success is too much, but it isnt.

After 60 days: -2×HP, chance of recovery 67.38%
Chance of surviving second threshold: 25% (two rolls at 50%)

So, there's only a 25% chance of you going bellow -1×HP (with another 25% chance of death and 50% chance of recover), and in that the chance that you'll survive 2 death rolls is only of 25%, but you have a total overall chance of 67.38% of recovering all the way up to that point.

So, 52.62% - Recovery before -HT
25% - Death
25% - 67.38% chance of recovery total - another 31.17% chance of recovering for the next 20 rolls(therefore, another 7.79% chance of recovery on top of the initial 52.62%, for a total recovery percentage of 60.41% which excludes the previous 25% of dead ones), with another 50% chance of death at this stage (so total death chance is increased by another 12.5% for 32.5% total chance of death.). So, in total, more or less 20% of the total initial sick wont go to the next phase, with 12.5% dying and 7.5% recovering (more or less), so only 5% go to the next stage, of which 1/3 will recover (close to 1%) and half of the other 2/3 die (so more or less 2%), and only 2% go to the last stage. And yes, my math is getting more laxed now, but nevertheless death rate remains between 30-35% rates

And on and on, until reaching either -5×HP (and dying with no roll) or finally rolling 3 or 4 and beggining to recover.

Adding up all the probabilities, the chances of survival are pretty close to 65%, so very very close to our mark. But that means that the sick can get all the way down to -49 HP until finally having the luck to come back from the gates of death and surviving!



Now, if recovery requires however that you hit 3, 4 or 5 on a roll, you get the following table:

HT 10
Success Chance (3, 4 or 5)
Number of Rolls

__1._____2._____3._______4.______5.______6._______ 7.__
4.63%_9.05%_13.26%_17.27%_21.10%_24.76%_28.24%

__8._______9._____10.______11._____12.____13.__
31.56%_34.73%_37.75%_40.64%_43.38%_46.01%

__14._____15._____16._____17._____18._____19.__
48.51%_50.89%_53.16%_55.33%_57.40%_59.37%

__20.__
61.25%

So, as you can see, if the roll to stop the infection requires rolling 5 or less, there's a 61.25% chance for recovering on at most 20 days, which is very very close to the mark of 40% death rate, while in the same period you'll suffer an average of 10 HP of damage, with 30% (31.17% actually) chance of having at least 1 critical failure in that time.

I think however that this covers well an infection with 40% of reducing a HT 10 average human to HP 0.

To actually die thou, I wont do the math, but by head I believe it would "only" kill on some 15% of times with a roll of 3, 4 or 5, so you can use those values to adjust exactly how letal you want it to be.

Also, you can declare that, for each TL above 6 (including 6), that roll increases by 1.

So, at TL6 a roll of 5- ends the infection if super letal or 6- if not so letal, at TL7 it's 6- or 7- and at TL8 it's 7- or 8-, which means that modern antibiotics turn infections annoying but hardly letal no more (chances bellow 0.1%)

[mlangsdorf]

From B444: "On a failure, the wound is infected. Treat this as any other disease. A typical infection requires a daily HT roll, modified as above, with failure indicating the loss of 1 HP. Most infections progress until the victim either makes a HT roll, ending the infection, or takes so much injury that he dies."

So the average HT 10 person has a 97% chance of surviving an infection with 5 HP or less of injury. I don't know where you're getting the idea that you need a critical success to throw off an infection. Unless you're proposing that as a revision to the existing rules.

I think your math is wrong, though. If an infectee rolls HT daily, loses 1 HP on failures, and kicks the disease on success by 6+ (ie, a 3 or 4), 55% of the HT 10 infected population will kick the infection before day 41. Infectees are, on average, losing 1/2 HP per day and hitting -1xHP at day 28-42, depending on luck and how injured they are. Of those that hit -1xHP, half of them will survive, for a fatality rate around 22%. Though some (roughly 22%) of the survivors will still be infected and make another death check around -2xHP (days 48-62 or so) but I'd only expect about 7% of the original population to die at that point, putting the total fatality rate around 35%.

The roll to resist injury from infection should probably also be penalized. Like I said, I'm not sure what the correct numbers should be, and someone who cares should probably run some Monte Carlo simulations across a range of values and get some semi-reasonable number.

[KarlKost]

Originally Posted by mlangsdorf

From B444: "On a failure, the wound is infected. Treat this as any other disease. A typical infection requires a daily HT roll, modified as above, with failure indicating the loss of 1 HP. Most infections progress until the victim either makes a HT roll, ending the infection, or takes so much injury that he dies."

So the average HT 10 person has a 97% chance of surviving an infection with 5 HP or less of injury. I don't know where you're getting the idea that you need a critical success to throw off an infection. Unless you're proposing that as a revision to the existing rules.

I think your math is wrong, though. If an infectee rolls HT daily, loses 1 HP on failures, and kicks the disease on success by 6+ (ie, a 3 or 4), 55% of the HT 10 infected population will kick the infection before day 41. Infectees are, on average, losing 1/2 HP per day and hitting -1xHP at day 28-42, depending on luck and how injured they are. Of those that hit -1xHP, half of them will survive, for a fatality rate around 22%. Though some (roughly 22%) of the survivors will still be infected and make another death check around -2xHP (days 48-62 or so) but I'd only expect about 7% of the original population to die at that point, putting the total fatality rate around 35%.

The roll to resist injury from infection should probably also be penalized. Like I said, I'm not sure what the correct numbers should be, and someone who cares should probably run some Monte Carlo simulations across a range of values and get some semi-reasonable number.

I originally only had placed the stats up to HP 0. But I fixed that going over all the way towards -1×HP and -2×HP and beyond. I edited the above post with the full math.

And read what OP has posted. He said he believes the rules for infections are too mildly, and that it's both too easy to recover and too hard to die from, which doesnt translate all too well to reality. So yes, I gave an idea to get closer to the real numbers of more or less 40% death rate.

[Curmudgeon]

Originally Posted by Michael Thayne

B444 says that a "typical" infected wound requires daily HT rolls, with failure costing 1 HP and success halting the infection. I wonder if this is too generous—most of the time you'll only take 1 or 2 points of damage before succeeding on that HT roll, and while the damage from infection might be enough to force an additional death check from a bad injury, there's basically no risk here of a relatively minor injury developing into something that kills you. In contrast, the bleeding rules require three successful HT rolls rolls, consecutively, such that if you succeed, then fail, then succeed, then fail, then succeed, you're still bleeding. Plus, there's a penalty to the HT roll for especially big wounds.

My question is: what's the best way to give "generic infection" some real teeth? Replacing the HT roll with an HT-3 roll would make infection very roughly as dangerous as bleeding. But I don't have a good sense either of what's realistic, or what makes for good gameplay. It seems to me that good gameplay demands that if you're bothering to use the rule at all, the danger should be serious enough to make players care about infection, and worry about getting wounded comrades proper medical care, even if most of the time it turns out to be a minor annoyance. But good gameplay might also demand somewhat less deadly rules than are strictly realistic. Thoughts?

The rules probably aren't being overly generous as regards survivability of wound infections, for relatively modern TLs, roughly TL 6+ when sulfa drugs and anti-biotics start to be widely available, so physicians are no longer just treating symptoms and hoping. They're even fairly reasonable for tL 5, once sterilization starts to be common.

For TL 4-, the issue is less that the rules aren't appropriate and more that you're likely to have more than one infection present at the same time. If you look up the different possible infections that a wound could develop, set up each infection as a disease under GURPS rules, and inflict as many of those infections on the characters as seems appropriate to the situation, you should come out with something approximating historical fatality rates. Whether it is worth that much bother is up to you.

[Michael Thayne]

Originally Posted by Curmudgeon

The rules probably aren't being overly generous as regards survivability of wound infections, for relatively modern TLs, roughly TL 6+ when sulfa drugs and anti-biotics start to be widely available, so physicians are no longer just treating symptoms and hoping. They're even fairly reasonable for tL 5, once sterilization starts to be common.

For TL 4-, the issue is less that the rules aren't appropriate and more that you're likely to have more than one infection present at the same time. If you look up the different possible infections that a wound could develop, set up each infection as a disease under GURPS rules, and inflict as many of those infections on the characters as seems appropriate to the situation, you should come out with something approximating historical fatality rates. Whether it is worth that much bother is up to you.

You already get a bonus for antibiotics. If the flat HT roll is already reasonable assuming antibiotics, that reinforces that making it an HT-3 roll is probably reasonable, given that antibiotics give a +3 bonus to the roll.

[Pursuivant]

Originally Posted by Varyon

Wound Size (note in all cases, if the GM decides it doesn't break the skin - such as for a smooth bludgeon - there's no chance of infection)

This is realistic, but what matters more than wound severity is wound surface area and available blood flow to the damaged area. For example, burns are particularly prone to infection because a burn is usually all on the skin and the underlying tissue might be damaged, limiting blood flow.

Perhaps give an additional -1 for 2+ hit locations damaged, -2 for 4+, -3 for whole body damage, -1 for burn or corrosive damage up to HP/2, -2 for burn/corrosive damage up to HP, -4 for burn/corrosive damage of -HP or greater.

Closed bruises and deep tissue damage can be prone to infection, or the equivalent, due to tissue necrosis. Any sort of scratch might be enough to let infectious organisms in and the body can't always fight them off if they get into dead or dying tissue.

So, maybe +1 to HT rolls for closed (i.e., HP/2 or less) crushing injuries.

Originally Posted by Varyon

Initial Infection

This is a good way to make nasty infections even nastier. Don't get a gunshot or a stab wound in a horse pasture or a sewer.

Blood flow at the wound site also has an effect on severity of infection. Perhaps give +1 for head injuries which don't involve the brain, or chest injuries which don't involve the Vitals, or for non-crippling hand injuries. -2 for penetrating (HP/2 or greater) hits to the Abdomen, Groin, or Pelvis. -1 for hits to the Feet, -1 for piercing, small piercing, large piercing, or impaling damage. Add +1 for Bleeding from the wound, since lots of blood might wash away some of the pathogens.

OTOH, overall blood loss reduces infection fighting and healing ability, since it takes white cells etc. time to regenerate. Maybe -1 for 0 to -HP, and -1 per multiple of -HP beyond that.

Originally Posted by Varyon

Multiple Successes to Recover

You could base number of rolls needed to shake off the infection based on initial MoF. That makes nasty infections not only harder to resist, but also harder to shake off and slower to heal.

[Pursuivant]

FWIW, GURPS 3E Compendium II has rules for Tetanus, which can simulate a really nasty infection other than gangrene/gas gangrene.

Summarized:

Roll vs. HT once per day for 21 days, at +1 per 3 days since the wound.

Infection means the victim loses 1 HT per day until he is at 2/3 HT. At that point contractions begin to appear and they begin to lose 2 HT per day unless a liquid diet or IV feeding is available. Roll vs. HT every 3 days (or HT+1 if the onset was more than one week, +2 if more than 2 weeks). Success regains 1 HT, critical success regains 3. Failure means normal loss for that day. CF means 2 HT lost. Daily HT loss drops to just 1 HT per day if the victim is restored to 2/3 HT or better, even if HT subsequently drops. The victim recovers when HT returns to normal. At -HT or less, roll to avoid dying using the same HT modifier as for onset.

This being GURPS 3E you can read HP for HT.

These rules are really nasty since with 21 rolls there's a fair chance of a Critical Failure, even with the +1 bonus/3 days and you lose 3 HT before you can make HT rolls to try to shake off the infection.

[Celjabba]

Originally Posted by mlangsdorf

From B444: "On a failure, the wound is infected. Treat this as any other disease. A typical infection requires a daily HT roll, modified as above, with failure indicating the loss of 1 HP. Most infections progress until the victim either makes a HT roll, ending the infection, or takes so much injury that he dies."

So the average HT 10 person has a 97% chance of surviving an infection with 5 HP or less of injury. I don't know where you're getting the idea that you need a critical success to throw off an infection. Unless you're proposing that as a revision to the existing rules.

If they fail the initial roll and the wound get infected, you can rule that the following daily rolls have the -2 penalty for "infected matter" present ("modified as above" in the rule text), unless the wound is cleaned daily.
And cleaning a deep (impaling, piercing, internal) wound require surgery, which per Bio-tech and Low-tech reintroduce the -2 for "infected matter" again if proper sterilization isn't used.

So, if they fail the initial roll (at HT+3 or HT+1 depending on the cleanliness of the wound), all subsequent rolls are at HT-2 with low-TL medicine. 'And a possible -3 for jungle and other "fever" areas)

Furthermore, you can decide as GM that a specific infection give an attribute penalty as symptoms (per B443).
A single -1 to all attributes rolls for being "feverish", and the odds became much worse, especially combined with the above.

Also, once they get to negative hp, starvation and especially dehydration will finish the job quickly, once the victim get unconscious/to weak to sustain themself.

[hal]

This was written for GURPS 3rd Edition Revised, but should also work for GURPS 4th edition.it works on the basis of lowering the character's effective saving rolls vs HT by a given amount. Once infection sets in for a given wound, no further healing rolls for that wound are possible. Until the body throws off the infection, no hit point damage for that wound can heal. In a nutshell, infections are defined not as damage to the hit points of a character, they're treated as levels of penalty to the Character's HT stat. The longer the infection runs, the worse the HT penalty. Sadistic GMs may wish to inflict further hit point damage to a specific wound on any failed HT rolls to shake an existing infection off, that fails by 3+.

Gangrene is defined as that state, by which a character's HT stat due to infection, has reached -4. Thus, a wound to the vitals or abdomen, is already serious due to the initial (optional) rule of penalizing the roll by -1 if the location is vitals or abdomen.

One thing to note: antibiotics should help in the saving rolls to end an infection. An optional rule to add might be TL-2 if the physician makes a successful roll vs the physician skill. Honey was known to some physicians as a natural aid against infection, even if the germ theory was unknown. One noted historical figure suffered massive lower jaw injuries, had the wound treated with honey and survived. Unfortunately, some infections that occur as a result of surgery (which technically is a wound!), when gained in a hospital, are antibiotic resistant. Unless you're trying to kill off a character, I'd avoid that issue entirely

Sepsis was a major contributor to death, so much so, that more people died of infections during war, than died outright of the wounds themselves. The mouth area is particularly susceptible to infections, that septicemia of the mouth was not uncommon. Any infection that spreads to another area (that 1 in 6 chance in the Harnmaster to GURPS article, is sepsis by definition.

Adding a little Harnmaster to GURPS

For those who are interested, check out what sepsis is vs septicemia

[KarlKost]

Originally Posted by hal

This was written for GURPS 3rd Edition Revised, but should also work for GURPS 4th edition.it works on the basis of lowering the character's effective saving rolls vs HT by a given amount. Once infection sets in for a given wound, no further healing rolls for that wound are possible. Until the body throws off the infection, no hit point damage for that wound can heal. In a nutshell, infections are defined not as damage to the hit points of a character, they're treated as levels of penalty to the Character's HT stat. The longer the infection runs, the worse the HT penalty. Sadistic GMs may wish to inflict further hit point damage to a specific wound on any failed HT rolls to shake an existing infection off, that fails by 3+.

Gangrene is defined as that state, by which a character's HT stat due to infection, has reached -4. Thus, a wound to the vitals or abdomen, is already serious due to the initial (optional) rule of penalizing the roll by -1 if the location is vitals or abdomen.

One thing to note: antibiotics should help in the saving rolls to end an infection. An optional rule to add might be TL-2 if the physician makes a successful roll vs the physician skill. Honey was known to some physicians as a natural aid against infection, even if the germ theory was unknown. One noted historical figure suffered massive lower jaw injuries, had the wound treated with honey and survived. Unfortunately, some infections that occur as a result of surgery (which technically is a wound!), when gained in a hospital, are antibiotic resistant. Unless you're trying to kill off a character, I'd avoid that issue entirely

Sepsis was a major contributor to death, so much so, that more people died of infections during war, than died outright of the wounds themselves. The mouth area is particularly susceptible to infections, that septicemia of the mouth was not uncommon. Any infection that spreads to another area (that 1 in 6 chance in the Harnmaster to GURPS article, is sepsis by definition.

Adding a little Harnmaster to GURPS

For those who are interested, check out what sepsis is vs septicemia

Egyptians used honey but also rotted bread to treat infections, which they didnt know that had penicilin but that they knew it healed.

Could honey and rotted bread confer a similar bonus to at least TL6 antibiotics? (ie Penicilin basically)