Saturday, April 27, 2019

Bring Out Your Dead (Disease in Twilight: 2000)

This is another in the series of posts exploring the various "mini-game" mechanics within the Twilight: 2000 v2.2 rule-set, this time the "unseen" threat of diseases - a threat that can't be solved with bullets alone. I suspect diseases are underutilised in most campaigns, possibly because of their threat to player agency and the usual emphasis on combat as conflict resolution.

Like a lot of the game mechanics, the rules for diseases are based on a  complex combination of different dice rolls and sub-systems which can be difficult to appreciate the impact of without working through examples and/or using the rules in extended play.

Plague: Carting the Dead, by J. Moynet (Wikki Commons)

The White Horse: Disease

"The horseman on the white horse was clad in a showy and barbarous attire. [...] While his horse continued galloping, he was bending his bow in order to spread pestilence abroad. At his back swung the brass quiver filled with poisoned arrows, containing the germs of all diseases." 
Vicente Blasco Ibáñez, "the Four Horsemen of the Apocalypse"

Disease is considered an important "scenario generator" in the game, likely more so than many RPGs - although the nuclear exchange and war inflicted heavy casualties, it was the resultant infrastructure breakdown and outbreaks of disease that dropped the global population to 50% or less in some areas. In the resulting Twilight World, the threat of disease remains ever present and is suggested to drive stories other than just straight "shoot and loot" conflict.

By my calculations, a disease very commonly affects settlements the group may encounter - almost 1 in 4 settlements if using the random crisis recommendation (see comment below).

Disease rules are given on pages 244-245 of the v2.2 corebook, with specific details of the various disease on the following two pages. The whole "mini-game" mechanics for disease are particularly complex, even when compared to other "non-combat" threats such as running out of fuel, vehicle breakdowns, starvationfatigue, and radiation.

Other than this main section the only references are in the Biology (people/water), Medical: Diagnosis (draft animal/people/water), Survival (water), and Tracking (wild animal) skill descriptions of the difficulty levels for detecting disease.

Medical: Diagnosis (EDU) overall is the most relevant skill, not only because it aids with recognising contamination across animals, people and water but also as it is used to diagnose the correct disease and modifies the recovery roll for the infected character. As Medical is a "cascade" skill, characters with Medical: Trauma Aid or Surgery have some skill with Medical: Diagnosis.

Catching a Disease

There are three ways to contract a disease:

  • People encounter (Biology or Medical: Diagnosis check)
    • Settlement (includes merchants, army groups; possibly marauders, hunters)
    • Encampment (includes refugees, stragglers; possibly marauders, hunters)
  • Animal encounter  
    • Draft animal (Biology or Medical: Diagnosis)
    • Wild animal (Tracking check while on the trail)
  • Drinking contaminated water/food (Biology, Medical: Diagnosis  or Survival check)

Note: it's not explicit in the actual Encounter section but the implication is that Disease should be checked for *every* relevant encounter eg Animal, Group, or Settlement. The risk of a particular people or animal encounter (or water) carrying a disease is given on the various tables on page 274 of the corebook.

Disease Frequency and Type Tables 
(Twilight: 2000 v2.2, page 274)

People: contracting a disease is dependent on the sanitary conditions - "settlement" reflects groups that practice good sanitation and so includes merchants, army groups and possibly more organised marauders and hunters. "Encampment" reflects less sanitary conditions and applies also to refugess, stragglers and some marauder / hunter groups. The base chance for "settlement" is 11+ on 2D6 or 8.34% (1 in 12) and for "encampment" is 16.67% (1 in 6).

Note: if using the Settlement Crisis suggestions, any settlement that rolls of "9" (Epidemic, doctor needed) or "10" (Disease, medicine needed) indicates a potential risk of contracting disease above and beyond the tables. So even if there's only about a 10% chance on average of disease for a given settlement/encampment, there's still a 20% chance (1 in 5) that it's been affected by disease in some way, further underlying the frequency of disease as a potential threat. Taken together, this is a 28% chance (roughly 1 in 4) of disease (recent, current or imminent) being an issue for any given settlement.

Animal: the base chance of an animal carrying a disease is 5.56% (1 in 20).

Water: this refers to water away from settlements including rivers, lakes, streams, springs, abandoned wells. The risk is the same as for animals ie. 5.56% (1 in 20). If detected the contaminated water can be avoided or boiled to avoid exposure - this would seem to be sensible and standard practice for any military trained characters with Survival skill.

Detecting Disease

Detecting a disease is an AVG difficult skill check (x2 Attr+Skill), with the skill applicable depending on the encounter as noted above:

  • Biology (EDU) is used for animals, people and water
  • Medical: Diagnosis (EDU) is used for draft animals, people and water
  • Survival (INT) is used for water
  • Tracking (INT) is used for wild animals

Medical: Diagnosis (or Biology) is the most useful skill for detection, and although Biology is also used to manufacture antibiotics, Medical (any) has much broader use. Tracking for wild animals seems to refer to identifying a diseased animal before the encounter in order to completely avoid them, I'd consider that once encountered Biology and Medicine: Diagnosis could be used instead.

A character with at least a "Novice" level Asset (Attribute + Skill = 9) in one of the relevant skills above therefore has a 90% chance of identifying a disease, with Experienced or higher level characters with the correct Asset capable of *automatically* detecting disease.

Even an unskilled character with a high EDU or INT Attribute level (8+ for example) has a reasonable rate of success at 40% (difficulty level is doubled from AVG to DIFF as unskilled).

Risk of Infection

Encountering a contaminated individual, animal or water alone is not enough to risk infection depending on how the disease is spread, it depends on whether they are exposed to one of it's modes of transmission (page 245):

The Referee should consult the description of the disease to determine how it is spread and compare this with the group's particular vulnerabilities. A disease spread by tainted food is not spread to those who don't eat the food, and one spread by contact doesn't affect those who do not make contact with the victim. A disease spread through the air places all characters within range at risk. 
As noted above, boiling contaminated water before drinking removes the risk of infeciton, even if the presence of disease is not detected - this applies to dysentery, cholera, hepatitis-A, typhoid fever, and possibly minor waterborne diseases. Only dysentery and typhoid are normally contracted from "wild" water sources however, the other waterborne diseases result from encampments/settlements.

Resisting infection is an AVG Constitution check (2x Attribute) on d20, with the target score modified as follows based on how vulnerable the character is and the disease's virulence:
  • -1 for each Fatigue level (includes those from starvation)
  • -x depending on the disease's "Infection Number" (up to 6)

For most unfatigued characters with an average CON of 5 for a target of 10 or less, the base risk is therefore 50% ie 50% chance of catching the disease if exposed. As most diseases have an "Infection Number" of at least 3, this reduces the target to 7 and gives the character a 65% (2 in 3) risk of contracting the disease. More virulent diseases (those with Infection Numbers of 5+ like Cholera, Pneumonia and Pneumonic Plague) increase this risk to 75% (3 in 4) for an average character.

Characters with weak base health such as a CON score of 2 or 3, have a high susceptibility to disease as their base chance of avoiding contracting infection is 30% or less, before the modification from the disease's Infection score! 

It's easy to see how Fatigue and starvation can rapidly lead to infection even in normally strong fit characters - as each Fatigue level reduces CON by 1 *and* reduces the Asset by another -1, the risk of infection rapidly escalates and easily spreads in communities or groups of soldiers without food even if they start with good health (reflected by a high CON score of 8+).

Note: the example on page 245 using Monk is wrong, his target should be 12-2-3 or 7 as the AVG difficulty should double his CON of 6 - the worked example uses a base of 5. So if he rolled a 4 on d20 he would have actually avoided contracting the disease. 

Diagnosis & Misdiagnosis

Image: Snook 8 / Deviant Art
(Header for this article on ISIS and Ebola)

Overall, the specifics of the various diseases as presented in dense blocks of text are difficult to understand, so I've collated all the cramped text information into a table to analyze further:

Summary Disease Diagnosis table
(derived from pages 246-247 T2k v2.2 corebook)

Looking at the "Diagnosis" table, food/water contamination seem the most common mode of transmission, whereas typhus, rabies and bubonic plague are more specific and readily avoidable.  Only pneumonia and pneumonic plague are spread through the airborne route.

Pneumonic plague is the most virulent (Infection Score of 6) and the two most difficult to diagnose diseases are hepatitis A and typhoid fever, although the latter cannot be mistaken for a minor disease.

Diagnosis in phase I of the disease is a Medical: Diagnosis check; this is one step easier (FOR becomes DIFF, DIFF becomes AVG, AVG becomes EASY) in phase 2 of the disease. Most diseases can be misdiagnosed as a minor disease leading to ineffective treatment and potential dire results.

Effects, Treatment, and Death or Recovery

This is where it becomes complex. Again I think constructing a table helps for this section.

Each disease has an incubation phase (no effect / unable to diagnose), a phase 1 (harder to diagnose but easier to recover from) and a phase 2 (easy to diagnose but more severe, treatment *half* as effective and harder to recover from). Treatment begun earlier works better, so diagnosing the disease correctly early makes a significant difference.

Recovery rolls are a D10 that must exceed the "base recovery" number.

This is modified by:
  • + CON score (average +5, max +10)
  • + Medical: Diagnosis of the treating character (effectively up to +5) 
  • + bonuses from correct treatment (assumes correct diagnosis, up to +8)
  • -1 for inadequate food
  • -1 for inadequate shelter 

All the diseases have a "base recovery" number of 18 or more - assuming adequate food and shelter, a character with an average CON of 5 and an average roll of 5 or 6 still needs the benefit of the treating character's Medical: Diagnosis skill (effective max 5) and treatment to have a chance of recovery.

If a character fails a recovery roll during phase 2 they have a risk of actually *dying*. 

If the character does not die they suffer debility (modified by the recovery roll success or failure).

Summary Disease Treatment & Recovery table
(derived from pages 246-247 T2k v2.2 corebook)

Comments on Specific Diseases

Rabies particularly seems quite insidious and lethal - although potentially readily avoided, it has a long incubation period of *weeks* and it's "base recovery" is 26 with a death probability of 100% ie automatic death if recovery fails. Although the 14-day DE vaccine provides a +8 modifier, the D10 + CON roll still has a target of 18, relying heavily on the treating character's Medical: Diagnosis skill. Without the specific treatment (the rare vaccine), an infected character with CON 10 and an excellent roll of 10 on the D10 needs to be treated by a character with a Medical: Diagnosis skill of 8+. The prolonged debility period of 20 weeks is the longest of all the diseases presented.

The two plagues (bubonic and pneumonic) are also essentially lethal on a failed recovery roll with extended debility periods of 15 weeks each. The next most deadly is actually food poisoning, with a death probability of 50% and a difficult recovery roll although if a character survives, their debility period is relatively short at 2 weeks.

The other disease (including minor diseases) are rarely lethal and easier to recover from, with debility periods of 6 weeks or less and easier to source treatment options.

Tuberculosis is a notable omission as it's apparently very common in war scenarios. Although perhaps more insidious and slow, it's very difficult to treat with standard antibiotics and exacerbated by malnutrition and low immunity eg HIV infection.


Looking at the disease rules closely, I'd consider that disease as threat or potential stimulus for the player group probably deserves more of a show given the conditions of the Twilight World. I've not come across much mention of it in the Polish supplements I've looked through and if anything the conditions in Poland in the Twilight World of 2000 seem setup so that disease should be a common enough challenge encountered.

The detail and complexity of the rules in T2k v2.2 are considerable - 4 rolls to check if a character is infected and up to 5 rolls to check for recovery or death. On the one hand, this is probably one of the more comprehensive treatments in an RPG I've seen but on the other hand, it may be overly complex and present a barrier to its use during play.

Hopefully, the additional tables above help with this however and I think the whole "mini-game" can be summarised into set steps from the dense block of text (see the Appendix below).

Weighing up the probabilities and taking into consideration the resource-poor world, the role of disease in the game seems to be to help drive the player group towards larger towns and cities seeking advanced medical treatment or as a barrier to prevent them exploring in a particular direction.

You might have an APC, enough fuel, parts and food to make it to Bremerhaven and a good chance of dodging former Soviet soldiers if you keep off the roads but if one of you gets sick, say your mechanic, and you don't have the correct medicine that side trip into town may cost you precious time. Or do you make a decision to leave your plague-ridden companion behind...

Appendix: From Contact to Recovery (or Death) 

This is a summary of the "mini-game" of disease for easy reference by a Referee:

Contracting Disease

  • On an Animal or Group (people) Encounter check for presence of disease (2D6 roll)
    • Check if a character drinks potentially contaminated water (1 in 20 risk)
  • Determine the type of disease according to the relevant table (page 274 or above)
  • Check to see if the group detects the presence of a disease (Medical: Diagnosis or other)
  • Referee to rule to determine if a character is potentially exposed 
  • AVG:CON check to see if exposed character contracts the disease 
  • Wait for the incubation period to pass and then inform player of symptoms

Overall, this involves four rolls: a 2D6 roll (check for presence), a D10 roll (type of disease) and two D20 rolls (detection check, CON check to avoid disease). Potentially could be simplified into four D20 rolls.

Treating the Disease

  • In phase 1, check to see if the disease is diagnosed using Medical: Diagnosis
  • IF the correct diagnosis is made, apply modifiers and check for recovery at the end of phase 1
    • IF recovery roll is successful, then the character recovers and suffers the debility effects
    • IF the roll is unsuccessful, check again at the end of phase 2
      • IF the phase 2 recovery roll is successful, move to the debility phase
      • IF the phase 2 recovery roll is unsuccessful, check for death
        • IF the death check fails, the character dies
        • IF the death check succeeds, apply debility 
  • IF a misdiagnosis is made, apply any applicable modifiers and check for recovery
    • IF recovery roll is successful (unlikely),  then the character recovers and suffers the debility effects
    • IF recovery is unsuccessful, recheck diagnosis (half difficulty in phase 2)
      • IF correct diagnosis is made, apply correct treatment and check recovery
      • IF misdiagnosis still, check for recovery (less likely)
    • Otherwise follow the same steps as above until death or debility 

This requires at least two D20 checks (diagnosis and phase 1 recovery rolls) but if the character is misdiagnosed in both phases increases to four D20 checks (two diagnosis checks, two recovery rolls) and a D10 roll (check for death). The D10 death check could be converted into a D20.


  1. Perfect timing! I keep forgetting about making disease rolls. I was planning to make disease checks after the Kalisz op. That city is in such a poor state it seemed fitting.

    1. Given Kalisz has recently (within the last 3-4 months) been the scene of a major battle involving two large forces of several thousand men and possibly hundreds of tanks, it's likely to have been significantly damaged. Even as a major city in the T2k rules (up to 28,000 people, 5% militia ie up to 1400 armed men - Kalisz has a population of ~100k in 2000 by estimate so being a bigger settlement makes some sense), there will have been significant casualties and the rubble, unexploded shells and general disruption / food shortage would make the conditions well suited to the outbreak of an epidemic. I'd suggest that an epidemic outbreak in Kalisz is almost inevitable...

  2. Thanks for the tables, that's something I've never thought of!

  3. Look there's some great tables in the v2.2 rules but also way to much dense text which is difficult to grasp without poring over it first - the tables make it easier for me to understand what's going on in each section. I suspect part of what makes these (likely) lesser used sections less common is they are difficult to access without Referee effort and part of why I write these posts is about breaking that down and trying to distil out the elements that make for interesting stories / games.