The HD surveillance form provides for initial classification of the disease into one of six categories which correspond to the universal ICD-9-CM diagnosis codes for HD (030.0-030.3, 030.8, and 030.9). This method of reporting classification is completed more consistently than other disease classification methods on the HD Surveillance Form in the United States. The diagnosis code distribution of classifications registered in 2006 is shown in Table 4a. The majority (107/137, 78 percent) of U.S. cases are coded as either 030.0 or 030.1 and correspond to either lepromatous (50 percent) or tuberculoid (27 percent) disease respectively. Comparing these percentages to the 10 year trend of reported codes (Table 4b) shows no significant variation, and these 2006 reports are in keeping with earlier observations.

Most leprologists prefer the Ridley-Jopling classification system, which includes both the lepromatous and tuberculoid ends of the spectrum as well as the associated borderline- lepromatous, borderline-tuberculoid and an indeterminate classification. This can be important in terms of prognosis and follow-up for potential untoward reactions. Unfortunately, Ridley-Jopling classification data is frequently omitted from the surveillance form. Some clinicians may not know the disease classification when they report the case and others may be unaware of this classification system. The reported Ridley-Jopling classifications in 2006, and their 10 year trends, are shown in Tables 5a and 5b respectively. Consistent with the diagnosis code data the majority (44/113) of U.S. cases are classified a lepromatous, but a roughly equivalent number (50/113) express borderline forms of the disease.

The WHO assesses cases only as ‘Multibacillary’ or ‘Paucibacillary’. A category of Multibacillary cases can be created by combining the Borderline and Lepromatous classes from the ICM-9 codes. Likewise, Paucibacillary cases can be identified by grouping the remaining categories. For 2006, 72 (53 percent) of the reported cases are grouped as Multibacillary and 62 (45 percent) as Paucibacillary according to this classification scheme (Tables 6a). These data are in keeping with the ten year trend of reporting as summarized in Table 6b, and illustrated graphically for 2006 in Figure 7 and for the preceding 10 year period in Figure 8.