In the zombie situations I've read about, generally a thermal or nuclear warhead is often an option to eliminate an outbreak (although not a zombie situation, The Andromedra Strain, for instance). From a survivors standpoint, it's not the thing we would be hoping for. But from a command standpoint, at what point is sterilization worthwhile? If it was NYC a la I Am Legend, would the hesitate over using their sterilization device for fear of destroying a major city? If it was, say, Oklahoma City, that is, not of as much of a strategic importance, would they be more likely to authorize total sterilization?

1. Military Sterilization Options
A. Atomic Sterilization
-Atomic sterilization would probably be the most effective method I can think of for containing a Class 3 or above outbreak. Using a smaller tactical engagement warhead, a small to medium sized infection site could easily be cleansed.
B. Thermal Sterilization
-Although I am not well briefed on their modern combat applications (aside from removing combatants while preserving physical installations), thermal warheads could be useful for elimination of large numbers of reanimated entities. While a significant portion of romeo echos could be neutralized, their would still be the possibility that either the infection agent could be resistant to high temperatures (a valuable trait if it was to be utilized as a biological weapon). Also, although damage to structures would be reduced compared to an nuclear event, wooden structures would create firestorms and other serious damage.
C. Daisy Cutters
-Originally used in the 1970s to clear landing pads in the dense jungles of SE Asia, Daisy Cutter bombs could be used more as a tactical sterilization method than a strategic sterilizer. Delivered either by high capacity helicopter (Skycranes or perhaps modified Chinooks), or by large trucks, the warhead could be delivered to a site of heightened resistance with a five minute timer, capable of clearing several city blocks beyond recognition.
D. Chemical and Biological Sterilization
-Although it may initially seem counter intuitive to add more chemical and biological entities into a romeo echo situation (given the likely cause of the original outbreak), chemical and biological weapons could be the most effective non nuclear option. (SEE Itech Corporation Strategic Division Report 1435-B, 'Anti-Cellular Enzyme').

2. Civilian Sterilization Options
Simply put, civilians do not under nearly all circumstances, have any access to weapons with the capabilities required to sterilize any significant numbers of romeo echoes. During the Reagan Administration, intelligence reports began to circulate regarding a potential resumption of research regarding the so called 'Z-virus' by the Soviet Union. This was later revealed to be untrue, but rather a political ploy to try to provide the Soviet Union with more leverage for the upcoming SALT II treaties. However, certain higher level military leaders were advised to conduct a study regarding the feasibility of containment following an attack. Thus, Project Nimbus was created. Simulating a zombie outbreak, the Z-virus was replaced by a harmless, though exceptionally infections, form of the common cold, which was covertly deployed to several towns and cities across the country. Also, to provide a more detailed analysis of the human element, an entire community, dubbed Zombieburg unofficially, was erected in a remote corner of Baja California, and was home to a two week excercise codenamed 'Revelation'.

During the exercise, which highlighted the danger of the virus poignantly, three groups of personel were placed in the town: The infected; the civilians; and the military. Based on the infection rates acertained from the earlier infection simulations; civilians were randomly transferred to infected status. Although the majority of the results from Project Nimbus are obviously denied as well as classified; several unusual and unorthodox containment methods were created.
A. Petrol
-Although in an outbreak situation, gasoline would probably become a valued commodity, in the first two days of the Revelation excercise, several civilian groups independently detonated gas stations after luring numerous romeo echoes into the vacinity (obviously, the civilians did not actually detonate the gas stations, when close enough, the civilians informed the infected that they, and everything else within a 25 meter radius, had been neutralized)
B. Water
-By tapping into the pressurized water lines normally reserved for fire control, a large majority of civilians were able to hold of the infected until the ninth day of the simulation by using a fire truck, until the water main was comprimised.
C. Hydrogen
-By day twelve, the majority of the town had been deemed unrecoverably comprimised. Despite firm infected and civilian resistance, military forces were able to proceed to the mock up hydrogen gas facility, and initiated the final mass sterilization by simulating a detonation of the hydrogen reserves at the facility, escaping via airlift shortly before the main explosion would have occured. (Although circumstance had this option performed by the military, it could, in theory, be copied by civilians. However, this is unlikely, as the civilians would be likely unwilling to sacrifice themselves by initiating an explosion.