A method of analyzing biological data, the biological data containing expression values of a plurality of polypeptides in the blood of a subject, wherein each of the polypeptides is selected from the group consisting of CRP, IP-10, TRAIL, IL1ra, PCT and SAA, the method comprising: operating a hardware processor for executing computer program instructions stored on a computer-readable medium, said computer program instructions comprising: computer program instructions for calculating a distance d between a segment S ROI of a curved line S and an axis π defined by a direction, said distance d being calculated, perpendicularly to said axis π, between a point P on said axis π and a corresponding point on said curved line, said points being defined by a coordinate δ 1 along said direction; and computer program instructions for correlating said distance d to the presence of, absence of, or likelihood that the subject has, a bacterial infection, wherein when said distance d is above a predetermined threshold ω B, said computer program instructions determine that it is likely that the subject has a bacterial infection; wherein said coordinate δ 1 is defined as δ 1 = b 0 + b 1 D 1 + b 2 D 2 +... + φ 1, where b 0, b 1,... are constant and predetermined coefficients, where each of D 1, D 2,... is an expression value of one of the polypeptides, and where φ 1 is either zero or nonlinear with respect to at least one of the expression values; wherein said segment is defined between a minimal coordinate δ 1,MIN and maximal coordinate δ 1,MAX, said minimal and maximal coordinates corresponding to physiologically possible ranges of the expression values of the polypeptides; and wherein at least 90% of said segment is between a lower bound line f(δ 1)-ε 0 and an upper bound line f(δ 1)+ε 1, wherein said f(δ 1) equals 1/(1+exp(δ 1)), and wherein each of said ε 0 and said ε 1 is less than 0.5. computer program instructions for calculating a distance d between a segment S ROI of a curved line S and an axis π defined by a direction, said distance d being calculated, perpendicularly to said axis π, between a point P on said axis π and a corresponding point on said curved line, said points being defined by a coordinate δ 1 along said direction; and computer program instructions for correlating said distance d to the presence of, absence of, or likelihood that the subject has, a bacterial infection, wherein when said distance d is above a predetermined threshold ω B, said computer program instructions determine that it is likely that the subject has a bacterial infection; wherein said coordinate δ 1 is defined as δ 1 = b 0 + b 1 D 1 + b 2 D 2 +... + φ 1, where b 0, b 1,... are constant and predetermined coefficients, where each of D 1, D 2,... is an expression value of one of the polypeptides, and where φ 1 is either zero or nonlinear with respect to at least one of the expression values; wherein said segment is defined between a minimal coordinate δ 1,MIN and maximal coordinate δ 1,MAX, said minimal and maximal coordinates corresponding to physiologically possible ranges of the expression values of the polypeptides; and wherein at least 90% of said segment is between a lower bound line f(δ 1)-ε 0 and an upper bound line f(δ 1)+ε 1, wherein said f(δ 1) equals 1/(1+exp(δ 1)), and wherein each of said ε 0 and said ε 1 is less than 0.5.