If you find such a sentence in your writing, look for a noun or phrase that will clarify what this means and put it after this, turning this into an adjective:

Although malaria infects primarily the populations of developing countries, it is a problem of global significance. This latter fact is apparent in statistics about the disease.

Let’s say, though, that the writer does want to share statistics both about developing countries and about the world as a whole. In this case, she’d do better to write a compound sentence that contains two ideas of equal weight, and to change the singular adjective this to the plural these:

Malaria infects primarily the populations of developing countries, but it is also a problem of global significance. Both of these facts are apparent in statistics about the disease.

Occasionally pronouns precede what they refer to:

This is true: malaria kills millions.

This word order reverses the sequence that readers expect, so they can get impatient if they have to wait too long to find out what the pronoun refers to. Use a pronoun before its antecedent only for an occasional special effect.

Moreover, in the example above, the antecedent for the pronoun this is an entire clause. Some readers object when the pronouns this, that, these, those, and which are used to refer to clauses rather than to nouns and noun phrases.