部分否定还是全部否定？

Investigation and management of eczema: Bacterial and viral swabs should be taken where supra- infection is suspected. HSV may cause a widespread infection, eczema herpeticum; small, punched- out lesions within worsening eczema suggest secondary HSV infection. Skin scrapings to rule out secondary fungal infection should be considered. T otal and specific IgE and skin prick tests are not usually helpful. Patch tests should be performed if contact allergic dermatitis is suspected.

汗疱疹的检查和治疗：若怀疑有继发感染，应采集细菌和病毒拭子。单纯疱疹病毒（herpes simplex virus，HSV）可引起广泛感染，称为疱疹样湿疹；若湿疹恶化时出现小的穿凿样皮损，提示继发HSV感染。应可考虑刮取皮肤碎屑以明确有无继发真菌感染。血清总 IgE 和特异性 IgE 测定、皮肤点刺试验通常对诊断帮助不大。如果怀疑是特应性接触皮炎，应进行斑贴试验。

not usually 应该是部分否定还是全部否定？“常无效”还是“并不常有效”？语法上有判断标准码？谢谢