Pandemic vs pandemia

Early occurrences of 'pandemic[al]' as an adjective

An Early English Books Online search finds six matches for "pandemic*," the earliest of which is from 1610. From Mathew Stonham, A Treatise on the First Psalme (1610):

This sleeping while Gods labourers are sowing: that so the Enemy Satan may sow his Tares among the Wheat: it is alasse, and againe I say alasse, ouer-vsuall. Wherin the subtile mallice of the old-Serpent may appeare vnto vs, who being not able to keepe the Word from vs, as in the time of Ignorance, keepeth vs from the Word by this sleepy Negligence. It is Morbus pandemicus, a Pandemicall disease; common, ouer-spread, ordinary, vsuall, and that not in some, but (a thing to bee vttered with griefe) well nigh in all congregations, as the practise almost of all men proueth it, their consciences witnesseth it, the Pastors of God from the places of their function (to their griefe) haue too often obserued it, and God himselfe who is present Euer, and in all places, sleepeth neuer, and in no place, knoweth it, and will (without our amendment preuenteth it) no doubt punish vs for it.

From Alexander Leighton, Speculum Belli Sacri: Or The Looking-glasse of the Holy War (1624):

You are the Physitians, content not your selues with the bare theoricke, or generall rules, but apply your rules, and pick out particular medicines, for particular diseases, in particular subjects; for Chronical, pandemical, or Epidemical diseases. Haue your specifick rules and receits, discover the darke day, and the devouring people, wherewith wee are threatned; the day of the Lord is great and very terrible, who can abide it?

From a 1654 translation of Simeon Partlicius, A New Method of Physick: or, A Short View of Paracelsus and Galen's Practice (published in German in the early 1620s):

In respect of the Region, [1] Some [diseases] are scattered up and down here and there, and are called Sporadical. [2] Others are Common, and are called Pandemical.

...

Pandemical Afflictions. [1] Pandemical or Common Afflictions are such as invade men universally, and they are either En[de]mical, or Epidemical.

From John Rogers, Diapoliteia. A Christian Concertation with Mr. Prin, Mr. Baxter, Mr. Harrington, for the True Cause of the Commonwealth (1659):

But it is a wicked thing to appoint the equality simply, altogether according to to tother (i.e. upon the whole number, or Promiscous Chaos of the people.) And it appears from what happens, that no Commonwealth of this kind, hath stability, or can stand long! (mark that!) and the reason is this, because it is impossible from the first errour committed in the beginning (or first laying of the Commonwealth) there should not happen some extream evil, or other. Thus far for the sence (and sentence) of his own Oracle (to name no more) against such an unjust Equality of Pandemick Government and foundation; without distinction of Dignitaries, or discrimination of the Good from the Bad, as a very unadvised thing, that will certainly rob the well-affected of their Rights! give them up to the Dammees of the Times! and but put them into an equal capacity for present! and into an under-capacity for future! (or by unavoidable consequence, through over-balance of Number with their enemies! who so shall be sure, to swallow all up at once!

From Gideon Harvey, Morbus Anglicus: or, The Anatomy of Consumptions (1666):

Among diseases, some do more generally haunt a Country, by reason of a certain property of the air, produced through a particular influence of the climat; and the fuming of malign streams out of the earth ; whence such diseases are termed Endemick or Pandemick : Others, though they are general, do only rage at a certain season of the year, and therefore are called Eipidemick ; according to which descriptions we may properly style a Consumption both an English Endemick, and Epidemick ; the former, because of our consumptive climat, and the latter, because it's most raging in spring and fall, according to the dictate of Hippocrates ; Malum ver tabidis, itemque autumnus ; that is, the spring is bad for consumptives, and so is the fall.

It's a great chance we find, to arrive to ones grave in this English Climate, without a smack of a Consumption, Death's direct doore to most English hard Students, Divines, Physicians, Philosophers, deep Lovers, Zelots in Religion, &c. London's Weekly Bills number deep in Consumptions; the same likewise proving inseparable accidents (attendants) to most of the other Diseases; which instances do evidently bring a Consumption under the notion of a Pandemick, or Endemick, or rather a Vernacular Disease (a disease alwayes reigning in a Countrey) to England; that is a common disease owing its rise to some common external and perennal (lasting all the year) cause of a Countrey; as a Consumptive Air, or a Consumptive Dyet. viz. eating much Flesh, drinking Hopt drink, &c.

And from Gideon Harvey, The Disease of London, or, A New Discovery of the Scorvey Comprising the Nature, Manifold Differences, Various Causes, Signs, Prognostics, Chronology, and Several Methods of Curing the Said Disease by Remedies, Galenical and Chymical (1675):

These Praedicates certainly are not convertible with the fore-mentioned Diseases, and therefore ought not so rashly to be pronounced the Scorvey; which moreover is Endemick, the others Epidemick and Pandemick. Thus far no sensible error can be incurred, if upon comprise of the whole, these Diseases are conceded to be Scorbutick, in the same terms, as one may aptly explain a Pleurisie, an Empyema, an Inveterate Cough, and many other Pulmonic Diseases, Asthmatic, but not an Asthma; unless derived from Saline Scorbutic Procatarctic and Proegumenal Causes.

Eighteenth-century English dictionaries unanimously identify pandemick as an adjective. The wording in Samuel Johnson, A Dictionary of the English Language, fourth edition (1755/1773) is typical:

PANDEMICK. adj. {πας and δεμος.} Incident to a whole people. [Cited example:] Those instances bring a consumption, under the notion of a pandemick or endemick, or rather vernacular disease to England. [—]Harvey on Consumption.

The emergence of 'pandemic' as a noun

The earliest instance of pandemic as a noun that I've been able to find in a series of Google Books searches is from the 1832. From J. A. Allen, "Remarks on the Etiology and Character of Epidemics," in The Boston Medical and Surgical Journal (September 5, 1832):

Those diseases which have some strong resemblance in their general characters, and attack many individuals in a large extent of country at about the same time, are commonly called epidemics. If all, or about all the inhabitants of a country be similarly attacked, at or near the same time, with a particular complaint, it is more properly called a pandemic. When any particular section of a country is liable to produce diseases of a similarity of character in many individuals, they are said to be endemic ; and a complaint which is confined to any particular class of persons is said to be endemic to that class of persons.

Here, Allen has clearly made the choice to treat pandemic as a noun on the model of epidemic rather than as an adjective on the model of endemic.

From George Collier, The Code for Safety; Or, The Laws of Epidemics (1853):

When a disease traceable on the map of the world, and owing its origin to an epidemical controlling force, is observed to travel over a wide range of the earth's surface, through an atmosphere undergoing subtle changes as yet incomprehensible to mankind it is called a progressive epidemic. If it be very general, it has been called a pandemic. If it shows itself only in particular localities, it is said to be endemic.

Like Allen, Collier treats pandemic as a noun, in a situation where it appears in close company with epidemical (an adjective), epidemic (a noun), and endemic (an adjective). Collier's use of epidemical is interesting because it suggests that he considers epidemic to be exclusively a noun. It may also be noteworthy that Collier was British, whereas Allen was American.

From H. Hjaltelin, M.D., "On the Treatment of Virulent and Zymotic Diseases" (November 4, 1865), published in Edinburgh Medical Journal (January 1866):

We know very well from medical history that bad and dangerous pandemics and epizootics have very often visited Europe in former days, and will still continue to do so, notwithstanding all our sanitary measures, which only serve to mitigate them, and may render them less dangerous, but can never totally prevent unforeseen atmospheric and telluric agencies, which, in all time, have been the first promoters of all pandemic and epizootic diseases.

And from an untitled lead item in The Lancet (May 25, 1867):

The lessons of previous pandemics, as of the present, had yielded little good result, and we were doomed to witness again a perpetration of the condemned and often-proved futile modes of treatment. The epidemic [of cholera], when it burst forth amongst us, found medicine less prepared to meet it than sanitary science ; it ended, and medicine could only say that means often tried before, found useless, and suspected in the main to be harmful, had failed again.

Early instances of 'epidemic' as a noun

That the noun form pandemic owes its existence to the model of the noun epidemic, as suggested in a comment by site participant High Performance Mark beneath the posted question, seems highly likely—and that noun form has been in use since the late 1500s at least. The earliest instances of the noun form involve the ancient Greek work known in English as "the Epidemicks of Hippocrates."

From a 1599 translation of André Du Laurens, A Discourse of the Preseruation of the Sight: of Melancholike Diseases; of Rheumes, and of Old Age:

But if it may be granted me to mixe one dram of Phisick amongst the large masse of these Philosophicall and Poeticall sentences, I dare auouch that in the eyes wee perceiue and discerne, the whole estate of the health of the bodie. Hippocrates that sacred Oracle of Greece (which all the world as yet euen to this day hath in singular reuerence and rare admiration) hath obserued the same very well in his Epidemickes, and in his treatise of Prognostications he commandeth the Phisition, when he goeth to see the sicke par∣tie, to behold and looke well vpon the face, but chiefly vpon the eyes, because that in thē as in a glasse, is easily espied the strength or weaknes of the animal powers: if the eye be cleere and bright, it maketh vs well to hope: but and if it bee darke, withered, and clowdie, it presageth death.

Various English authors throughout the seventeenth century (and later) refer to Hippocrates' "Epidemicks." The word begins to appear as a common noun by the 1666. From Gideon Harvey, Morbus Anglicus: or, The Anatomy of Consumptions (1666):

And considering withall its malignity and contagious nature, it may be numbred among the worst of Epidemicks, or popular diseases, since next to the Plague, Pox, and Leprosy, it yields to none in point of contagion ; for its no rare observation here in England, to see a fresh coloured lusty young man yoakt to a consumptive female, and him soon after attending her to the grave.

From Πυρετολογια, or a history of Feavers (1674):

From which manner of admission [namely, through "venemous streams breathing from Mineral Exhalations"] into the Blood, according to the capacity of the Pores that receive it ; it also comes to pass, that Diseases (although very Venemous) are not so apt to communicate their Infection to some Bodies, as such that are in their own nature less dangerous ; we often find that ordinary Epidemicks though without any venemous Malignity, when any Procatartick cause hath pre-disposed the Body for their reception, are much more catching, though less Mortal.

...

Which intended Motion (giving the Heart that Perturbation we call the Feaver) holds till either the Febrile Matter, according to the proportion of its Particles, is precipitated, or otherwise Symptomatically carried off to some improper Sal- [line of text not visible] or else till the Morbisick Matter (which rarely happens in Epidemicks) by Coction separated from the useful parts of the Blood is reduced to such a position, as we call Putrefaction ; in which state being capable of seperation, it leaves the remaining Mass to circulate peaceably.

... notwithstanding that, as also their ordinary communication of themselves by Infection, I shall indeavour to vindicate from the imputation of Malignity, and to prove that their antecedent causes are from such an alteration in the Blood and Humours, as renders the Receptacles in either of them fit to receive such atomes as the preceding intemperance of the Season had (for the reasons delivered in the former Section) rendred of a Figure Discordant to the Pores of the Blood, which every Sex, Age, or Constitution being not always alike capable of doing, makes many of these Epidemicks more apt to seize either Children or more aged People, though for the most part the Morbisick Diathesis both of the Ambient Air and Internal Humours, is so universal, that but few of either Sex or Age, but (for the Causes I shall presently mention) may be obnoxious to it, and yet the disease carry nothing in it of venome, nor so much as an ordinary Malignity, more than what is caused by some error in managing it.

And from William Bacon, A Key to Helmont, Or, A Short Introduction to the Better Understanding of the Theory and Method of the Most Profound Chymical Physicians (1682):

Now what should e do? should we clog and fetter our Champion, the vitals, with nasty depauparating flegms and gross substances? or should we send proper and true assistance to him? I leave you to judg. I desire any impartial person to observe (in the Countrey, where many are so poor, as they cannot apply to Physicians) in Epidemicks, and see how many more dye of them, that use the common way of Physick, than of those that use none at all, though the latter commonly want all conveniencies.

...

I call God to witness, I give you here a faithful account what I am, and what my designs are : My Birth was generous, my education liberal, my dependances competent, bred by my Fathers command towards the Civil Law, though my natural inclination was towards Physiology ; to which I stuck close after I was emancipated by Marriage ; but at length, observing what ill success Physicians had, and that double as many recovered in Epidemicks, of the miserable poor people that had not money to go to a Physician, or conveniency of lodging, warmth, or other necessaries, as of thise that did, and had those conveniencies also ; my esteem for Medicine decreas'd more and more, and had absolutely despair'd that any good could be done by it, until I call'd to mind some very good Cures done by the Learned Dr. Edmund Dickenson ; ...

Conclusions

Epidemic seems to have emerged as a noun in English by 1599 in the form of a title of a medical work by Hippocrates—his Epidemics. The word began to appear as a common noun (still usually in plural form) by 1666. Meanwhile, the adjective pandemical began appearing in English texts no later than 1610, but pandemic didn't make the jump from adjective to noun until about 1832.

It seems likely that the example of epidemic as a noun figured prominently in the transition of pandemic from an adjective to a noun—a transition that endemic, for example, never made. It is far easier, however, to document that the transition occurred in the case of pandemic than to explain precisely why it occurred.

As for the alternative form pandemia, an Early English Books Online search turns up only three instances of that word—from 1640, 1656, and 1676—all of them in connection with Venus. An entry in John Lempriere, Bibliotheca Classica; or, A Classical Dictionary (1801) explains the genesis of this term:

PANDEMIA, A sirname of Venus, expressive of her great power over the affection of mankind.

The epithet Pandemia thus refers to Venus's sway over all people (pan + demos), implying that love was the first pandemic, if not the cause of the first pandemonium. It doesn't appear that pandemia in a medical sense, as an alternative to pandemic, ever had much currency in English.