program population;

const
total = 100; { Number of people in population}
stages = 15; { Number of stages}
Numsim = 5; {Number of simulations}
count = 3; {Number of encounters per stage}
tol = 0.28; {if sum on dice is less than 5 and person interacts with infected person, infection occurs}

var y: array[1..total] of integer; {Y holds the infection status of population}
   a: array[1..stages,1..Numsim] of integer; {a holds the number of infected people at each stage}
   sim,i,j,k,m,n,inner: integer; {each column of a is one simulation}
   FileName : string;    {Will record the output into OutFile you specify}
   OutFile: Text;


function Sum: integer;
var i,result : integer;
begin
   result := 0;
   For i := 1 to total Do
      result := result + y[i];
   Sum := result;  {sum is the summation of 1's in y}
end;


begin
   write('Enter Name of output File: ');
   Readln(FileName);
   Assign(OutFile,FileName+'.txt');
   Rewrite(OutFile);
   For sim := 1 to NumSim do {Do the simulation 5 times}
      begin
         Randomize;
         for n := 1 to total do
            y[n] := 0; {all people start out healthy (healthy - 0)}
            y[5] := 1; {An infected person!}
            for k := 1 to stages do
               a[k,sim] := 0; {a[k,sim] is the number of infected people at stage k, simulation sim}
            for k := 1 to stages do {begin simulation for each stage}
               begin
                  for inner := 1 to count do {each person has count encounters per stage}
                     begin
                        for n := 1 to total do {individual n interacts with another person}
                           begin
                              m := trunc(total*Random) + 1;
                              if y[m] = 1 then   {if individual m is infected}
                              if y[n] = 0 then {if individual n is not infected}
                              if random < tol then {if random number is less than tolerance}
                              y[n] := 1; {individual n is now infected!}
                           end; {loop on n}
                     end; {loop on inner}
                     a[k,sim] := sum; {sum the number of people infected at this stage}
               end; {loop on k (stage)}
         end; {loop on sim}
         for i:= 1 to stages do
            begin
               for j := 1 to sim do
                  write(OutFile,a[i,j],',');
                  writeln(OutFile);
            end;
         Close(OutFile);
end.

Here's a text file of the population program.