using System;
using System.Text.RegularExpressions;
public class Example
{
public static void Main()
{
string pattern = @"(无|否认)(既往)?[^,。，.]{2,6}过敏史";
string input = @"患者既往体质尚可，否认有“高血压、糖 尿病、冠心病”等慢性病病史，否认心、肝、脑、肺、肾“等重大脏器疾病史，否认”肝炎、肺结核等传染病史，否认其他重大手术及外伤史，否认输血及中毒史，呋喃唑酮过敏史，过敏表现：皮疹瘙痒、全身浮肿，否认食物药物过敏史";
RegexOptions options = RegexOptions.Multiline;
foreach (Match m in Regex.Matches(input, pattern, options))
{
Console.WriteLine("'{0}' found at index {1}.", m.Value, m.Index);
}
}
}
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for C#, please visit: https://msdn.microsoft.com/en-us/library/system.text.regularexpressions.regex(v=vs.110).aspx